Karthos, Monsterous Enemy

Whenever a creature you control dies, target
opponent sacrifices a creature. If it was a dragon,
they sacrifice three permanents instead. If they
can't they take damage equal to its power.
{1}{b}{r}, Sacrifice a creature: Draw a card. The
next creature you cast cost {x} less to cast, where
X is that creature's power.
"dominate the untamed, dominate the plane"
- Sheoldred