Break the private key, do a 30x leverage short and move the coins!
If you tank the market and create systemic insolvency then you might hold $1B of short contracts at an exchange where the operators have packed up and fled to anonymous sandy beaches, and for all your cleverness those contracts and $10 might buy you lunch tomorrow.
I understand we're doing thought experiments here, but I'd say the really tricky part is breaking the private key.
That's the interesting thing, you can try to brute force keys in general by just throwing enough money at the problem. Technology always advances and makes cryptography less secure.