mtg blue search your library for a card Rules Text: search, target, player's, library, exile, 21 cards not actual card. Trench Gorger [Commander 2011]

There are a myriad of ways to accomplish this, with some being easier than others

A Sultai value commander like Glarb, Calamity's Augur is probably a good shout

Agathas Soul Cauldron Targeted graveyard removal every turn for an initial cost of two is already extremely useful, and thats just the start of what Agatha can cook up with this cauldron

Norn's Choirmaster gives your Incubator tokens another buff with frequent proliferation

They serve to give your side of the board tempo by allowing your creatures to attack (removing defenders), giving you more time to set up the board (removing attackers/expensive creatures), and allow for combat tricks (saving your creatures after damage is on the stack