Zer0, A Number

Commander ninjitsu {x}{u}{b} (Create {x} 1/1 colorless assassin creature tokens with deathtouch named Zer0 Clone that are tapped and attacking.)

Deathtouch

Whenever Zer0 becomes the target of a spell, sacrifice it, and destroy all tokens named Zer0 Clone.

Zer0's power and toughness is equal to the number
of creatures you control with deathtouch.