Diamond Lion + First Day of Class + Dross Scorpion + Cauldron of Souls

Diamond Lion

First Day of Class

Dross Scorpion

Cauldron of Souls

How it works

1. Activate Cauldron of Souls, giving Diamond Lion persist until end of turn.
2. Activate Diamond Lion by tapping it, discarding your hand, and sacrificing it, adding three mana of any one color.
3. Diamond Lion's persist ability and Dross Scorpion both trigger.
4. Resolve the Dross Scorpion ability, untapping Cauldron of Souls.
5. Resolve the Diamond Lion's persist ability, returning it from the graveyard to the battlefield with a -1/-1 counter on it.
6. First Day of Class triggers, putting a +1/+1 counter on Diamond Lion and giving Diamond Lion haste until end of turn.
7. Repeat.