Kallmech, Unchained Cerberus

Hellbent — As long as you have no cards in
hand, Kallmech cost {7} less to cast.

Whenever another attacking creature you control dies, you may pay {b/r}. If you do, lose 3 life for each card in your hand. Then return that creature card from your graveyard to the battlefield tapped at the beggining of the next endstep. Do this only thrice
per turn.

"Nice Doggy!"