Coinbase, headquartered in San Francisco, is an online bitcoin broking exchange which caters to US, Canada, Europe, UK, Australia, Singapore. Up to 150 US dollars and pounds can be bought on Coinbase on a daily basis. It charges a 3.99% on all the exchanges via credit or debit card. Coinbase offers very high limits. Limits depend on your account level, which is determined by how much information you have verified. Fully verified U.S. customers may buy up to $50,000 worth of bitcoin daily.
  •   A decline in the adoption of bitcoin could have a negative effect on the price of bitcoin and bitcoin-related investments. Bitcoin’s adoption has been on a generally continuous climb since bitcoin first gained mass media attention in 2013. However, there can be no guarantees this growth will continue. Further, adoption of bitcoin as a means of payment has been limited when compared with the increase in the price of bitcoin, indicating that the majority of bitcoin’s use is for investment and speculative purposes. A lack of acceptance of bitcoin as a means of payment could negatively impact the price of the Bitcoin Futures contracts in which the Fund invests.
Let’s say Larry owns one bitcoin and the current price is $16,600, be believes the price is overdone to the upside for a short period of time.  This is a fictional example, so don’t beat me up on the outlook, you can criticize Larry, but he’s made up too.  Larry has a futures account and sees that he can sell short a January XBT Future at $17,600.  He decides to do this and is now short 1 January XBT Future at $17,600. 
The Fund generally does not expect to invest directly in futures contracts, option contracts and swap agreements (“Bitcoin Instruments”). The Fund expects to gain exposure to these investments by investing a portion of its assets in the ProShares Cayman Bitcoin Futures Strategy Portfolio, a wholly-owned subsidiary of the Fund organized under the laws of the Cayman Islands (the “Subsidiary”). The Subsidiary is advised by ProShare Advisors, the Fund’s investment advisor, and invests directly in Bitcoin Instruments. Unlike the Fund, the Subsidiary is not an investment company registered under the 1940 Act. The Fund’s investment in the Subsidiary is intended to provide the Fund with exposure to commodity markets related to bitcoin in accordance with applicable rules and regulations. The Fund will invest up to 25% of its total assets in the Subsidiary. Except as otherwise noted, references to the Fund’s investment strategies and risks include the investment strategies and risks of the Subsidiary.
On March 18, 2013, the Financial Crimes Enforcement Network (“FinCEN”) a bureau of the US Department of the Treasury, issued interpretive guidance relating to the application of the Bank Secrecy Act to distributing, exchanging and transmitting “virtual currencies.” More specifically, it determined that a user of virtual currencies (such as bitcoin) for its own account will not be considered a money service business (“MSB”) or be required to register, report and perform recordkeeping; however, an administrator or exchanger of virtual currency must be a registered money services business under FinCEN’s money transmitter regulations. As a result, Bitcoin Exchanges that deal with U.S. residents or otherwise fall under U.S. jurisdiction are required to obtain licenses and comply with FinCEN regulations. FinCEN released additional guidance clarifying that, under the facts presented, miners acting solely for their own benefit, software developers, hardware manufacturers, escrow service providers and investors in bitcoin would not be required to register with FinCEN on the basis of such activity alone, but that Bitcoin Exchanges, certain types of payment processors and convertible digital asset administrators would likely be required to register with FinCEN on the basis of the activities described in the October 2014 and August 2015 letters. FinCEN has also taken significant enforcement steps against companies alleged to have violated its regulations, including the assessment in July 2017 of a civil money penalty in excess of $110 million against BTC-e for alleged willful violation of U.S. anti-money laundering laws.
The SEC staff also has acknowledged that, while a board of trustees retains ultimate responsibility, trustees may delegate this function to an investment adviser. The Board of Trustees has delegated this responsibility for determining the liquidity of Rule 144A restricted securities that may be invested in by a Fund to the Advisor. It is not possible to predict with assurance exactly how the market for Rule 144A restricted securities or any other security will develop. A security that when purchased enjoyed a fair degree of marketability may subsequently become illiquid and, accordingly, a security that was deemed to be liquid at the time of acquisition may subsequently become illiquid. In such an event, appropriate remedies will be considered in order to minimize the effect on the Fund’s liquidity.
Various government agencies, departments, and courts have classified bitcoin differently. China Central Bank banned the handling of bitcoins by financial institutions in China in early 2014.[69] In Russia, though cryptocurrencies are legal, it is illegal to actually purchase goods with any currency other than the Russian ruble.[70] Regulations and bans that apply to bitcoin probably extend to similar cryptocurrency systems.[71]
Credit Default Swaps (“CDS”): In the case of a CDS, the agreement will reference one or more debt securities or reference entities. The protection “buyer” in a credit default contract is generally obligated to pay the protection “seller” an upfront or a periodic stream of payments over the term of the contract until a credit event, such as a default, on a reference entity has occurred. If a credit event occurs, the seller generally must pay the buyer: a) the full notional value of the swap; or b) the difference between the notional value of the defaulted reference entity and the recovery price/rate for the defaulted reference entity. CDS are designed to reflect changes in credit quality, including events of default. The CDS Short North American HY Credit ETF will normally be a “buyer” of CDS (also referred to as a buyer of protection or a seller of risk). The CDS Short North American HY Credit ETF will primarily invest in centrally cleared, index-based CDS that provide credit exposure through a single trade to a basket of reference entities. The CDS Short North American HY Credit ETF may also invest in single-name CDS. Single-name CDS provide exposure to a single reference entity and are not centrally cleared.
Crypto Facilities and the CME Group  have been calculating and publishing the Bitcoin Reference Rate (BRR) since November 2016. Such an official rate is a prerequisite of options trading in the traditional markets. The BRR is calculated based on the rates from the biggest exchanges: Bitstamp, GDAX, itBit, and Kraken. More concretely, it is calculated based on all Bitcoin vs. USD trades on the participating exchanges between 3 and 4 p.m. London time. To calculate the BRR, the hour between 3 and 4 is divided into 12 intervals of 5 minutes. For each interval, the volume-weighted median of the Bitcoin price is calculated (statistically, the median, in contrast to the average, prevents single outliers from distorting the price). The BRR is then the average of these 12 median values. More details about the calculation of the BRR can be found in the BRR whitepaper.
In the course of providing advisory services, the Advisor may simultaneously recommend the sale of a particular security for one account while recommending the purchase of the same security for another account if such recommendations are consistent with each client’s investment strategies. The Advisor also may recommend the purchase or sale of securities that may also be recommended by ProFund Advisors LLC, an affiliate of the Advisor.

To illustrate the point, recall that futures markets are just counterparty contracts. Let's say I want to SHORT the market and profit off a decline in BTC/USD. If I put an order to sell Weekly futures contract at $400, and someone buys that offer, then we have created a futures contract. If it goes down, I profit and he loses, if it goes up, he profits and I lose. However, what if price goes down really fast, and my counterparty only had a little margin backing his position? Well, he gets margin-called when it goes down enough, and the system takes his contract and forces it to be sold to a different counterparty that wants to take the LONG side of my contract.
Over the past several years, a number of Bitcoin Exchanges have been closed due to fraud, failure, security breaches or governmental regulations. The nature of the assets held at Bitcoin Exchanges make them appealing targets for hackers and a number of Bitcoin Exchanges have been victims of cybercrimes. In many of these instances, the customers of such Bitcoin Exchanges were not compensated or made whole for the partial or complete losses of their account balances in such Bitcoin Exchanges. No Bitcoin Exchange is immune from these risks but the existence of these risks has created a higher barrier of entry for new Bitcoin Exchanges. The loss of confidence in new and smaller Bitcoin Exchanges and in the Bitcoin Exchange Market overall can slow down the mass adoption of bitcoin. Further, the failure of the Bitcoin Exchange Market or any other major component of the overall bitcoin ecosystem can have consequences for the Bitcoin Network, have an adverse effect on the price of bitcoin and could have a negative impact on the Bitcoin Instruments in which certain of the Funds invest.
Although shares of the fund are listed for trading on a stock exchange and may be listed or traded on other U.S. and non-U.S. stock exchanges, there can be no assurance that an active trading market for the Fund’s shares will develop or be maintained. Trading in shares on an exchange may be halted due to market conditions or for reasons that, in the view of an exchange, make trading in shares inadvisable. In addition, trading in shares on an exchange is subject to trading halts caused by extraordinary market volatility pursuant to exchange “circuit breaker” rules. Short selling of shares is also limited pursuant to SEC rules if the trading price of shares varies by more than 10% from the previous day’s closing price on the exchange. There can be no assurance that the requirements of the exchange necessary to maintain the listing of the Fund will continue to be met or will remain unchanged or that the shares will trade with any volume, or at all, on any stock exchange.
The Funds may invest in a combination of forward currency contracts and U.S. dollar-denominated market instruments in an attempt to obtain an investment result that is substantially the same as a direct investment in a foreign currency-denominated instrument. This investment technique creates a “synthetic” position in the particular foreign currency instrument whose performance the manager is trying to duplicate. For example, investing in a combination of U.S. dollar-denominated instruments with “long” forward currency exchange contracts creates a position economically equivalent to investing in a money market instrument denominated in the foreign currency itself. Such combined positions are sometimes necessary when the money market in a particular foreign currency is small or relatively illiquid.
Unitary Fee Funds    S&P 500 Dividend Aristocrats ETF, S&P MidCap 400 Dividend Aristocrats ETF, Russell 2000 Dividend Growers ETF, MSCI EAFE Dividend Growers ETF, MSCI Europe Dividend Growers ETF, MSCI Emerging Markets Dividend Growers ETF, Decline of the Retail Store ETF, Long Online/Short Stores ETF, DJ Brookfield Global Infrastructure ETF, Large Cap Core Plus, S&P 500 Ex-Energy ETF, S&P 500 Ex-Financials ETF, S&P 500 Ex-Health Care ETF, S&P 500 Ex-Technology ETF, Equities for Rising Rates ETF, High Yield—Interest Rate Hedged, Investment Grade—Interest Rate Hedged, Managed Futures Strategy ETF, K-1 Free Crude Oil Strategy ETF (the “Crude Oil Strategy ETF”), Bitcoin Futures Strategy ETF, Short Bitcoin Futures Strategy ETF, Blockchain/Bitcoin Strategy ETF, and Bitcoin Futures/Equity Strategy ETF
(c) distribute with respect to each taxable year at least 90% of the sum of its investment company taxable income (as that term is defined in the Code without regard to the deduction for dividends paid—generally, taxable ordinary income and the excess, if any, of net short-term capital gains over net long-term capital losses) and net tax-exempt interest income, for such year.
Below is a description of various types of money market instruments and other debt instruments that a Fund may utilize for investment purposes, as “cover” for other investment techniques such Fund employs, or for liquidity purposes. Other types of money market instruments and debt instruments may become available that are similar to those described below and in which the Funds also may invest consistent with their investment goals and policies. Each Fund may also invest in pooled investment vehicles that invest in, and themselves qualify as, money market instruments.
Transaction fees payable to the Trust are imposed to compensate the Trust for the transfer and other transaction costs of a Fund associated with the issuance and redemption of Creation Units of Shares. A fixed Transaction Fee is applicable to each creation or redemption transaction, regardless of the number of Creation Units purchased or redeemed. In addition, a variable Transaction Fee equal to a percentage of the value of each Creation Unit purchased or redeemed may be applicable to a creation or redemption transaction. Purchasers of Creation Units of the Matching and Ultra ProShares Funds for cash may also be required to pay an additional charge to compensate the relevant Fund for brokerage, market impact or other expenses. Where the Trust permits an in-kind purchaser to substitute cash in lieu of depositing a portion of the Deposit Securities, the purchaser will be assessed an additional charge for cash purchases. The maximum Transaction Fee on purchases and redemptions will be 2.00% of the NAV of any Creation Unit, except that for the High Yield—Interest Rate Hedged, the Investment Grade—Interest Rate Hedged and the Short Term USD Emerging Markets Bond ETF, a Transaction Fee up to 3.00% will be charged on the cash used in lieu of depositing all or a portion of the Deposit Securities or the cash portion of any redemption transaction. The Transaction Fees charged to each Fund are presented in the Authorized Participant Handbook.
  •   Changes in the Bitcoin Network could have an adverse effect on the operation and value of bitcoin, which could have an adverse effect on the value of Bitcoin Futures Contracts and the value of Fund Shares. The open source nature of the Bitcoin protocol permits any developer to review the underlying code and suggest changes to it via “Bitcoin Improvement Proposals”, or “BIPs.” If accepted by a sufficient number of miners, BIPs may result in substantial changes to the Bitcoin Network, including changes that result in “forks.” Such changes may influence the price of Bitcoin and Bitcoin Futures Contracts. In particular, it is possible that the price of the Bitcoin Futures Contracts subsequent to a “fork” may be linked to the price of bitcoin on only one of the resulting Bitcoin Networks, rather than the aggregate price of bitcoin on all resulting Bitcoin Networks. The CBOE Futures Exchange (“CFE”) and Chicago Mercantile Exchange (“CME”) have announced different protocols for addressing forks.

Poloniex is an asset exchange based in the US. Trading on Poloniex is secure and allows traders to explore new and trendy coins which are up for speculation. It offers high volume margin trading and lending service for major crypto assets. Reportedly, the largest user base for trading on this site comes from Russia (6.06%) and US (24.84%). A differentiating factor about the site is that it does not support fiat currency.
The information in this Prospectus is not complete and may be changed. Shares of the Funds may not be sold until the registration statement filed with the Securities and Exchange Commission is effective. This Prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Commodity Swaps. Commodity swaps are used either as substitutes for owning a specific physical commodities or as a means of obtaining non-leveraged exposure in markets where a specific commodity is not available. Commodity swaps provide the Fund with the additional flexibility of gaining exposure to commodities by using the most cost-effective vehicle available.

The Fund may invest in stocks of large-cap companies. Although returns on investments in large-cap companies are often perceived as being less volatile than the returns of companies with smaller market capitalizations, the return on large-cap securities could trail the returns on investments in smaller and mid-sized companies for a number of reasons. For example, large-cap companies may be unable to respond quickly to new competitive challenges, such as changes in technology, and also may not be able to attain the high growth rate of successful smaller companies.
To purchase or redeem through the Clearing Process, an Authorized Participant must be a member of NSCC that is eligible to use the Continuous Net Settlement system. For purchase orders placed through the Clearing Process, the Authorized Participant Agreement authorizes the Distributor to transmit through the Funds’ transfer agent (the “Transfer Agent”) to NSCC, on behalf of an Authorized Participant, such trade instructions as are necessary to effect the Authorized Participant’s purchase order. Pursuant to such trade instructions to NSCC, the Authorized Participant agrees to deliver the requisite Deposit Securities and the Balancing Amount to the Trust, together with the Transaction Fee and such additional information as may be required by the Distributor.

However, many of these investors are still waiting to be convinced to take the leap into crypto. One thing that is still giving many institutional investors pause is the fact that trade management systems in the crypto world simply do not offer the sophistication they are used to in conventional trading. They’ve become accustomed to the support of reliable automated tools, and the prospect of working without those can be a serious roadblock.

Maintenance Margin - this is the % of the position value you have to have in your account at the very minimum to avoid being Margin Called.  In some exchanges, margin call will mean you get notified and must deposit more margin to avoid liquidation (like CryptoFacilities). On other exchanges you will at this point be liquidated out of your position. So if maintenance margin is 5%, then the 0.05 BTC of your initial margin will need to be kept for the position to be alive.
For purchases and sales of derivatives (i.e., financial instruments whose value is derived from the value of an underlying asset, interest rate or index) the Advisor evaluates counterparties on the following factors: reputation and financial strength; execution prices; commission costs; ability to handle complex orders; ability to give prompt and full execution, including the ability to handle difficult trades; accuracy of reports and confirmations provided; reliability, type and quality of research provided; financing costs and other associated costs related to the transaction; and whether the total cost or proceeds in each transaction is the most favorable under the circumstances.

There's a lot of ins and outs which can get confusing in arbitrage trading. We won't go into the technicals of why futures contracts trade at a premium to spot price. You can read a full explanation here. If it's not of interest to you, all you need to know is that there's a tendency, the further out in time the futures contract expires, for the premium to spot to be higher and higher in nominal percentage terms.