Shivergeist

Whenever Shivergeist deals damage to a creature,
tap it. It doesn't untap during its controller's
next untap step. You may pay {2}{u}{b}. If you
do, put a -1/-1 counter on it.

"I found Jenkins dead of frostbite in his hammock, his fingers and toes missing like the others'. I fear I am
going mad, as I hear something clanking in the ice
caves. Perhaps it is the thing that killed him. I will
lie in wait tonight.
- Notes recovered from a Cryspeak expedition