Kundo, Master Warrior

Bushido 1 (Whenever this creature blocks or becomes
blocked, it gets +1/+1 until end of turn.)

Flanking (Whenever a creature without flanking
blocks this creature, the blocking creature gets -1/-1
until end of turn.)

At the beginning of each combat, exile the top card
of your library. You may cast that card without
paying its mana cost as long as Kundo, Master
Warrior is blocking or being blocked.