Blue-Horned Unicorn

Persist (When this creature dies, if it had no -1/-1 counters on it, return it to the battlefield under its
owner's control with a -1/-1 counter on it.)
Whenever Blue-Horned Unicorn deals combat
damage to a player, you may discard a card. If you
do, put X +1/+1 counters on Blue-Horned
Unicorn where X is the converted mana cost of
the discarded card.