A Bear Bitcoin ETF would not be such a bad bet.

As assuming it tracked bitcoins using the CME futures there is a 10-20% per year roll benefit.

Meaning that the ETF return would not be the same a -BTC price but would be -BTC price +15% per year.

So as long a Bitcoin went up by less than 15% a year you would make money. So you are betting Bitcoin will below $100k in 3 years time.

A brave bet but not an unreasonable one.

Dec13->Dec17 it went from $1000 to $700