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.
At the expiration of the contract you are trading, all positions get closed out and settled. Different exchanges use different anchors to settle against. To avoid manipulation, most of them use an index. OKCoin uses a custom 6-exchange index (3 chinese, 3 Western), while BitMEX, Deribit, Coinpit, and CryptoFacilities use a multi-spot-exchange Index to settle all of its contracts at expiration. This minimizes the risk of any manipulation if contracts settled on a single exchange's price, but it also makes it more difficult to manage your hedges since there's no way to "buy" or "sell" an index. No system is perfect, and each one offers different unique pro's and con's, just like your selection of contract type and length. So depending on your case you may want something different than someone else.
EDIT: #10 Bonus (Suggested by @kerstenwirth ) — always check the ticker symbol. Ticker symbols are not universal, and may vary from exchange to exchange in rare cases. Those cases, though, can come back to bite you. For example, Bitcoin Cash trades on some exchanges as BCH, while it trades on others as BCC. BCC is also the ticker symbol for BitConnect, which was recently outted as a Ponzi Scheme. If you bought BCC under the impression was Bitcoin Cash, you would’ve lost a lot of money.
Two members of the Silk Road Task Force—a multi-agency federal task force that carried out the U.S. investigation of Silk Road—seized bitcoins for their own use in the course of the investigation.[86] DEA agent Carl Mark Force IV, who attempted to extort Silk Road founder Ross Ulbricht ("Dread Pirate Roberts"), pleaded guilty to money laundering, obstruction of justice, and extortion under color of official right, and was sentenced to 6.5 years in federal prison.[86] U.S. Secret Service agent Shaun Bridges pleaded guilty to crimes relating to his diversion of $800,000 worth of bitcoins to his personal account during the investigation, and also separately pleaded guilty to money laundering in connection with another cryptocurrency theft; he was sentenced to nearly eight years in federal prison.[87]
If a beneficial owner of Fund Shares who or which is a foreign shareholder has a trade or business in the United States, and income from the Fund is effectively connected with the conduct by the beneficial owner of that trade or business, such income will be subject to U.S. federal net income taxation at regular income tax rates and, in the case of a foreign corporation, may also be subject to a branch profits tax.
I used to find it odd that these hypothetical AIs were supposed to be smart enough to solve problems that no human could, yet they were incapable of doing something most every adult has done: taking a step back and asking whether their current course of action is really a good idea. Then I realized that we are already surrounded by machines that demonstrate a complete lack of insight, we just call them corporations. Corporations don’t operate autonomously, of course, and the humans in charge of them are presumably capable of insight, but capitalism doesn’t reward them for using it. On the contrary, capitalism actively erodes this capacity in people by demanding that they replace their own judgment of what “good” means with “whatever the market decides.”
The Bitcoin Network and bitcoin, as an asset, currently hold a “first-to-market” advantage, often referred to as a “network effect,” over other digital assets. This first-to-market advantage has resulted in the Bitcoin Network evolving into the most well developed network of any digital asset. The Bitcoin Network enjoys the largest user base of any digital asset and, more importantly, the largest combined mining power in use to secure the Bitcoin Blockchain. Having a large mining network enhances user confidence regarding the security of the Bitcoin Blockchain and long-term stability of the Bitcoin Network. Despite the marked network effect advantage of the Bitcoin Network over other digital assets, it is possible that real or perceived shortcomings in the Bitcoin Network, technological, regulatory or other developments could result in a decline in popularity and acceptance of bitcoin and the Bitcoin Network.
On top of that, the cryptocurrency market travels at lightspeed compared to other markets. New coins enter the market on a daily basis (in 2016, there were about 550 different coins, today there are about 1,500), and each one has news every day. I’m not doubting your ability to consume and analyze news, but that level of information bombardment will always be more effectively consumed as a group. In these communities, you’ll see members link news and relevant articles about coins you’ve invested in and coins you’ve never heard of. The community will definitely expand your knowledge much faster than doing it all yourself.

State the general effect of any contract, arrangements or statute under which any director, officer, underwriter or affiliated person of the registrant is insured or indemnified against any liability incurred in their official capacity, other than insurance provided by any director, officer, affiliated person, or underwriter for their own protection.

This may sound like an unfair system to those who are used to trading with confidence that their profits are settled in full, but it's a compromise that has been made in order to offer the high leverage. If you want to guarantee that your profits are not reduced by any socialised loss, then use CryptoFacilities or Coinpit. They use a "termination" procedure in the event of a margin call not being filled. This simply terminates the contract and sends the portfolio value of the losing counterparty to the winning counterparty. It's worth noting that the system has been incredibly robust, with very minimal socialised losses being triggered on OKCoin and none on BitMEX as of November 2015.
In addition, the securities of some foreign governments, companies and markets are less liquid, and may be more volatile, than comparable securities of domestic governments, companies and markets. Some foreign investments may be subject to brokerage commissions and fees that are higher than those applicable to U.S. investments. A Fund also may be affected by different settlement practices or delayed settlements in some foreign markets. Moreover, some foreign jurisdictions regulate and limit U.S. investments in the securities of certain issuers.

Assume it is January 3, 2015. Bob and Ann both want to trade at Bitcoin Futures Exchange (BFE). BFE offers 3 different contracts: one expiring and settling on Friday January 9 ('weekly'), another expiring Friday January 16th ('biweekly'), and finally one expiring in March 27 ('quarterly').  Each contract is worth 1 bitcoin notionally.  BFE has a policy that traders have to put 20% of margin down to enter a trade, so Bob and Ann deposit 0.2btc to their BFE accounts as they only want to trade 1 contract.

Those who believe in Cryptocurrency claim it to be the next big thing in the history of mankind. The mere fact that Cryptocurrency is beyond the control of any government body gets it a lot of eyeballs. Imagine a universal currency beyond the control of liquidity, inflation and government subsidy. This would mean that the commercial activity of economies working on Cryptocurrency shall be privatized absolutely.
By now you may ask yourself, “If I think that the price of an asset is going to rise, why should I buy a call option and not the asset itself?” The answer is this: Options give you leverage. That means that with a limited amount of capital, you can profit much more by buying options than assets – but also lose much more. This is because a small difference in the price of the underlying asset immediately leads to a substantial change in the price of the derivative. For example, when pork belly prices rise from 1,000 USD to 1,100 USD (an increase of 10%), call options for 1,000 USD suddenly become much more valuable – their prices may rise from 10.5 USD to 105 USD. Thus, if you have invested all of your capital in pork bellies, you will win 10% – if you have invested in pork belly call options, you will pocket a 1,000% profit.