General Grievous

Ward {2}

Whenever you cast an artifact spell, amass Droids X, where
X is that spell’s mana value. (Put X +1/+1 counters on an Army you control. It’s also an Artifact and a Robot. If you don’t control an Army, create a 0/0 black artifact Droid Army first.)

Sacrifice an artifact: Return another artifact from a graveyard to the battlefield under your control. You may only activate this ability only once per turn and only when you could cast a sorcery.