When Michelangelo enters, create a Mutagen token. (It's an artifact with ", , Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")
If one or more +1/+1 counters would be put on a creature you control, that many plus one +1/+1 counters are put on it instead.
Michelangelo is a 2-mana mono-green counters payoff: every time you'd add +1/+1 counters to your creatures, you add one extra, snowballing your board out of control. You ramp early, deploy counter engines and proliferate effects, then turn an overgrown creature sideways or go wide with anthem-sized tokens. The free Mutagen token gives you immediate value and an extra counter the turn he lands.
Cheap commander that comes down turn 2 and immediately threatens a fast counters snowball
The replacement effect stacks with every counter source, including proliferate and the Mutagen
Mono-green has the best ramp, the deck can rebuild and recast a cheap commander easily
Fits the resilient, grindy counters plan that doesn't rely on a single combo card
Mono-green lacks interaction, removal, and card-quality fixing for opposing threats
Strategy is creature-centric and folds to board wipes
No evasion or protection built in, so a buffed-up beater gets chump-blocked or removed
The +1 bonus only triggers when counters are actually being placed; do-nothing turns happen without enablers
Legendary Creature — Mutant Ninja Turtle
, 
, Sacrifice this token: Put a +1/+1 counter on target creature. Activate only as a sorcery.")