Rockimus, Terror Unleashed

When Rockimus, Terror Unleashed enters the battlefield, destroy target artifact or creature.
Whenever an artifact or creature is destroyed by a card effect, put a +1/+1 Counter on Rockimus, Terror Unleashed.
Partner with Dexter, Eternal Beloved (When this creature enters the battlefield,
target player may put Dexter into their hand from their library, then shuffle.)
Companions Forever (You can have two commanders if the other is Dexter.)