BitMEX is a bitcoin futures site which is 100% anonymous and uses only bitcoin, no fiat or altcoins. But you can use bitcoin to trade the changes in ETHBTC price from Poloniex. That means when Ethereum is pumping, you can profit off it using your bitcoin by longing.
Also if you're feeling lucky, you can try shorting the top, but Ether has trolled a lot of people lately with that, so be careful!
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