Infinite creature LTBInfinite creature ETBInfinite creature sacrifice triggersInfinite death triggersInfinite mana creatures you control can produceInfinite untap of creaturesInfinite +1/+1 counters on a creature
How it works
Activate Xu-Ifit by tapping it, returning a creature card from your graveyard to the battlefield.
When the creature enters the battlefield, Intruder Alarm triggers, untapping all creatures.
Activate Bloodflow Connoisseur by sacrificing the creature returned in step 1.
Repeat.
This crafty little loop turns Xu-Ifit, Osteoharmonist into a relentless necromancer by exploiting Intruder Alarm's global untap trigger every time a creature enters the battlefield. Once Xu-Ifit brings back a fallen creature, the resulting untap lets you immediately sacrifice that returned creature to Bloodflow Connoisseur to pump up its +1/+1 counters and ready Xu-Ifit to tap again. Because the resurrected creature loses all its abilities under Xu-Ifit's care, you can safely recur it over and over to continuously feed the Connoisseur.