If you want to speculate on the price of a cryptocurrency then the use of a Contract for Difference (CFD) is an option to consider. You won’t actually own the cryptocurrency, which means you don’t face the hassle and hurdles of trying to buy via one of the unregulated exchanges. Instead, a CFD is a financial instrument which allows you to speculate on price movements.
These are NOT linked to or related in any way, to the futures contracts that trade on the CME or CBOE.  Not every article I have read makes this clear.  So the bright side of this story is that the contracts listed and traded on U.S. exchanges were not involved.  That is encouraging from both a regulatory aspect and for the future potential growth of cryptocurrency linked products in the U.S.

Under normal market conditions, each Fund intends to invest substantially all of its assets in Benchmark Futures Contracts. The contractual obligations of a buyer or seller holding a futures contract to expiration may be satisfied by settling in cash as designated in the contract specifications. Alternatively, futures contracts may be closed out prior to expiration by making an offsetting sale or purchase of an identical futures contract on the same or linked exchange before the designated date of settlement. Once this date is reached, the futures contract “expires.” The Funds do not intend to hold bitcoin futures contracts through expiration, but instead to “roll” their respective positions. “Rolling” refers to a process whereby futures contracts nearing expiration are closed out and replaced with an identical futures contract with a later expiration date. Accordingly, the Funds are subjects to risks related to rolling.
Margin Call - when you run out of bitcoin on your account to cover the contract positions you have taken (your account value doesn't cover the Maintance Margin) you are officially rekt. Some exchanges like CryptoFacilities will merely notify you that you have to deposit more or reduce your positions to increase your margin. Others like BitMEX will liquidate you at this level where the exchange takes over your position to liquidate it into the market to prevent system loss.
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.

The Board of Trustees of the Trust reserves the right to declare a split or a consolidation in the number of Shares outstanding of any Fund, and may make a corresponding change in the number of Shares constituting a Creation Unit, in the event that the per Share price in the secondary market rises (or declines) to an amount that falls outside the range deemed desirable by the Board.
No Independent Trustee (or an immediate family member thereof) during the two most recently completed calendar years had: (i) any material interest, direct or indirect, in any transaction or series of similar transactions, in which the amount involved exceeded $120,000; or (ii) any direct or indirect relationship of any nature, in which the amount involved exceeded $120,000, with:

S&P 500 Dividend Aristocrats ETF; S&P MidCap 400 Dividend Aristocrats ETF; Russell 2000 Dividend Growers ETF; Equities for Rising Rates ETF; Morningstar Alternatives Solution ETF; 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    4:00 p.m. (3:30 p.m. if in cash) in order to receive that day’s closing NAV per Share
ProShare Advisors, pursuant to a separate Management Services Agreement, performs certain administrative services on behalf of the Funds, such as negotiating, coordinating and implementing the Trust’s contractual obligations with the Funds’ service providers; monitoring, overseeing and reviewing the performance of such service providers to ensure adherence to applicable contractual obligations; and preparing or coordinating reports and presentations to the Board of Trustees with respect to such service providers as requested or as deemed necessary. For these services, the Trust pays to ProShare Advisors a fee at the annual rate of 0.10% of average daily net assets for each of the Funds. ProShare Advisors has entered into an Advisory and Management Services Fee Waiver Agreement that waives this management services fee for the Morningstar Alternatives Solution ETF through at least October 31, 2018. Prior to this date, ProShare Advisors may not terminate the arrangement without the approval of the Board.
Bitcoin futures contracts are a new type of futures contract that began trading in December 2017. Unlike the established futures markets for traditional physical commodities, the market for bitcoin futures contracts is in the developmental stage and has very limited volume, trading and operational history. Bitcoins and other cryptocurrencies are a new and developing asset class subject to both developmental and regulatory uncertainty. As such, bitcoin futures contracts and the market for bitcoin futures contracts may be riskier, less liquid, more volatile and more vulnerable to economic, market, industry, regulatory and other changes than more established futures contracts and futures markets. There is no assurance that a liquid market will emerge or be sustained for bitcoin futures contracts. The liquidity of the market for bitcoin futures contracts will depend on, among other things, the supply and demand for bitcoin futures contracts, the adoption of bitcoin and the commercial and speculative interest in the market for bitcoin futures contracts and the potential ability to hedge against the price of bitcoin with exchange-traded bitcoin futures contracts. Additionally, if market participants executing trades in bitcoin futures contracts face constraints, including capital constraints, security risks, or high execution costs, the price of bitcoin futures contracts may fail to capture price movements in the underlying price of bitcoin.
To seek its investment objective, as a cash reserve, for liquidity purposes, or as “cover” for positions it has taken, each Fund may invest all or part of its assets in cash or cash equivalents, which include, but are not limited to, short-term money market instruments, U.S. government securities, floating and variable rate notes, commercial paper, certificates of deposit, time deposits, bankers’ acceptances or repurchase agreements and other short-term liquid instruments secured by U.S. government securities. Each Fund may invest in money market instruments issued by foreign and domestic governments, financial institutions, corporations and other entities in the U.S. or in any foreign country. Each Fund may also invest in pooled investment vehicles that invest in, and themselves qualify as, money market instruments.

Government regulation could adversely impact the operation of the Bitcoin Network or the use of bitcoin. As bitcoin and other digital assets have grown in popularity and in market size, certain U.S. federal and state governments, foreign governments and self-regulatory agencies have begun to examine the operations of bitcoin, digital assets, the Bitcoin Network, bitcoin users and related issues. Although currently bitcoin is not regulated or is lightly regulated in most countries, including the United States, some countries have, and one or more countries may in the future, take regulatory actions that severely restrict the right to acquire, own, hold, sell or use bitcoin or to exchange bitcoin for fiat currency. Regulation in the U.S. and foreign jurisdictions may restrict the use of bitcoin or otherwise materially impact the global demand for bitcoin. Regulation of initial coin offerings (“ICOs”) and other cryptocurrencies may have an impact the price of bitcoin. If Bitcoin Exchanges become subject to regulation, that may also impact trading in bitcoin as trading may be concentrated in a smaller number of regulated exchanges, which may impact price, volatility and trading volumes. Also, most Bitcoin Exchanges currently require bitcoin trading accounts to be fully funded, but if margin trading is introduced, there may be additional risks, including
In the event an order is cancelled, the Authorized Participant will be responsible for reimbursing the Fund for all costs associated with cancelling the order, including costs for repositioning the portfolio, provided the Authorized Participant shall not be responsible for such costs if the order was cancelled for reasons outside the Authorized Participant’s control or the Authorized Participant was not otherwise responsible or at fault for such cancellation. Upon written notice to the Distributor, such cancelled order may be resubmitted the following Business Day, with a newly constituted Portfolio Deposit or Fund Securities to reflect the next calculated NAV.
BitMEX is a derivatives exchange that offers leveraged contracts that are bought and sold in Bitcoin. This is a platform that provides trading in bitcoin derivatives. The derivative traded is a perpetual swap contract, which is a derivative product similar to a traditional Futures Contract. Swap contracts trade like spots, tracking the underlying assets.
The Funds may make short sales “against the box,” i.e., when a security identical to or convertible or exchangeable into one owned by a Fund is borrowed and sold short. Whenever a Fund engages in short sales, it earmarks or segregates liquid securities or cash in an amount that, when combined with the amount of collateral deposited with the broker in connection with the short sale, equals the current market value of the security sold short. The earmarked or segregated assets are marked-to-market daily.
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 Short 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.
A futures contract is a technique to hedge positions and reduce the risk of the unknown. It is also used for arbitrating between current spot and future contracts. In the case of bitcoins, futures have been more associated with miners who face the risk of unknown future prices. OrderBook.net (formerly iCBIT), a futures marketplace operating since 2011, sells millions of futures contracts each month. The standard contract size (or tick size) is $10. A typical instrument would look like this: BTC/USD-3.14. Here "BTC/USD" signifies the rate of exchange between Bitcoin and US dollar, "3" means the month of March, and "14" signifies the year 2014. The trading symbol for the same instrument will be BUH4. Each month has a trading symbol like March is H (as per Chicago Mercantile Exchange), the "B" is taken from BTC and the "U" from USD, and "4" signifies the year.
Don’t FOMO. This is a spot that people most frequently lose money on. A dash of manipulation, two tablespoons of media hype, a cup of CME and CBOE announcements, and a generous handful of FOMO drove Bitcoin prices from $10,000 to $20,000 in December. Since that time, Bitcoin fell to a low of $9,000 and is currently sitting at around $11,000. It’s easy to look back and say, “if only I waited one month, then I could’ve bought at $9,000 instead of waiting for Bitcoin to hit $20,000 again for me to break even.” But the reality is, the combination of 1) being greedy, 2) investing blindly, and 3) FOMO were likely large contributors to the purchase at an all-time-high. Even in the crazy world of cryptocurrency, if a coin pumps that quickly, it will correct — it’s a matter of time. Speculative pumps are almost always followed by dips. While trying to jump onto a train going full speed sounds like something straight out of a James Bond movie, I’m sure most of us can agree we would probably save some limbs if we just waited for it at the next stop.
It bears repeating -- when trading futures on leverage, you are not "borrowing" the money, so you don't have to pay a financing rate on your positions. Even though you are 100x exposed, you don't have to pay 100x financing (unless you're trading the perpetual swap, which is not a futures contract, but has similar characteristics). Since bitcoin futures do tend to trade at a premium, you are in a way paying an implied interest rate in the contract, because if you want to go long, you have to pay above spot, so you pay the interest up front in the contract, in a way.
It’s reasonable to assume that a product named a future is attempting to predict the future. For Bitcoin futures, this is definitely not what they deliver. The core utility of the futures markets is not predicting the future prices of their product but rather the secure delivery of a product at a known price, quality, and date. If there’s product seasonality (e.g., specific harvest times) or foreseeable shortages/abundances then future’s prices may reflect that but neither of these factors applies to Bitcoin.
Bitcoin Gold (BTG) is the second fork from Bitcoin (i.e. the second version to stem from Bitcoin’s source code). It retains Bitcoin’s transaction history, meaning that if you owned Bitcoin before the fork, you now own the equal amount of Bitcoin Gold. This cryptocurrency aims to introduce an alternative mining algorithm that is less susceptible to ASIC-based optimization, therefore allowing users to earn more with their computer cycles.
Since you bought 68.4246 BTC, you want to short 68 BTC and lock in the USD value. You will have 0.4246 BTC left over, which will give you a slightly long bias. You can either fix this by only buying 68 BTC in step 1 or by giving yourself more short exposure by shorting 69 BTC. Remember that CryptoFacilities contracts are inverse (which allow locking in USD) and are denominated in BTC