Pactsworn Chorus

Whenever a player exchanges control of a creature, you may draw a card and put a chant counter on Pactsworn Chorus.
Whenever an opponent declares attackers, you may give any attacking creature -1/-1 until end of turn as long as there's at least 1 chant counter on Pactsworn Chorus. Repeat this process X times, where X is the number of chant counters on Pactsworn Chorus.
{3}{u}{b},{t}; Target player takes control of target creature you control until end of turn.