Blood Pet by sacrificing it, adding ({B} magic symbol) .
Resolve the
Altar of the Brood trigger, causing each opponent to mill two cards due to
Bruvac.
If an opponent mills a nonland card,
The Wise Mothman triggers, putting a +1/+1 counter on
Evolution Witness.
Evolution Witness triggers, returning
Blood Pet from your graveyard to your hand.
Repeat.
Notes
This combo fails if every card milled in step 4 is a land. Having more opponents reduces this chance significantly.
Bruvac is also not explicitly required but greatly increases the chances of the combo succeeding. If the combo does fail, you can place a +1/+1 counter on