Infinite +1/+1 counters on a creatureInfinite death triggersInfinite creature ETBInfinite creature LTBInfinite creature sacrifice triggers
How it works
Activate Antler Skulkin by paying 2, giving Callous Sell-Sword persist until end of turn.
Activate Ashnod's Altar by sacrificing Callous Sell-Sword, adding CC.
When Callous Sell-Sword dies, its persist ability triggers, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
Callous Sell-Sword enters the battlefield with an additional +1/+1 counter on it for each creature you controlled that died this turn.
Repeat.
This clever loop relies on Painter's Servant to paint all cards and permanents your chosen color, allowing Antler Skulkin to successfully target any of your creatures—including the normally non-white Callous Sell-Sword—with its persist-granting ability. Once Callous Sell-Sword has persist, you can feed it to Ashnod's Altar to generate colorless mana while sending it to the graveyard, which conveniently funds the next activation of Antler Skulkin. Every time Callous Sell-Sword returns with a -1/-1 counter, its own enter-the-battlefield trigger counters that penalty by granting it a +1/+1 counter for the creature that just died, neutralizing the counters so the loop can repeat indefinitely.