Basri's Lieutenant + Metallic Mimic + Ashnod's Altar

Basri's Lieutenant

Metallic Mimic

Ashnod's Altar

How it works

1. Activate Ashnod's Altar by sacrificing another creature with a +1/+1 counter on it, adding CC.
2. When the creature dies, Basri's Lieutenant's second ability triggers, creating a 2/2 Knight creature token that enters the battlefield with a +1/+1 counter due to Metallic Mimic.
3. Repeat.

This elegant loop turns a simple sacrifice outlet into an engine for infinite resources by leveraging the way counters and creature types interact on the battlefield. With Metallic Mimic set to choose Knights, every new token created by Basri's Lieutenant's death trigger enters with a +1/+1 counter already on it. This ensures that when you feed that token to Ashnod's Altar for two colorless mana, it dies with a counter and immediately triggers Basri's Lieutenant to replace it with another Knight.