Basri's Lieutenant + Master Biomancer + Phyrexian Altar

Basri's Lieutenant

Master Biomancer

Phyrexian Altar

How it works

1. Activate Phyrexian Altar by sacrificing another creature with a +1/+1 counter on it, adding one mana of any color.
2. When the creature dies, Basri's Lieutenant's second ability triggers, creating a 2/2 Knight creature token that enters the battlefield with at least two +1/+1 counters due to Master Biomancer.
3. Repeat.

This loop is a masterclass in recursive scaling, fueled entirely by the mana-generating engine of Phyrexian Altar. When you sacrifice a creature, Basri's Lieutenant steps in with its death trigger to replace it with a 2/2 Knight token, but that token doesn't arrive unprotected: Master Biomancer uses its own power to slap additional +1/+1 counters onto the incoming Knight right as it hits the battlefield. Because that fresh token now bears a +1/+1 counter, it's immediately primed to be sacrificed back to Phyrexian Altar, restarting the whole sequence to generate infinite colored mana, endless death triggers, and an ever-growing army of knights.