Saw in Half | Culling the Weak | Eternal Witness

Cards

Cast
Culling the Weak by paying ({B} magic symbol) and sacrificing another creature, adding ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) ({B} magic symbol) .
Cast
Saw in Half by paying ({2} magic symbol) ({B} magic symbol) , destroying
Eternal Witness and creating two token copies of it with base power equal to half the destroyed creature's power and base toughness equal to half the destroyed creature's toughness, rounding up each time.
When the
Eternal Witness tokens enter the battlefield, they trigger, returning
Saw in Half and
Culling the Weak from your graveyard to your hand.
Repeat.