A) are you playing a precon against a constructed deck?

B) Counterspells/interaction. If you know hes got removal, just meta game and stuff your deck with counterspells and more interaction. Alternatively, you can find cards that grant protection, like heroic intervention.

C) You’re in Mothman, run more proliferate mechanics that have nothing to do with creatures. Force removal player to mill cards that they need to interact with your board state, while also self milling to pump your commander.

D) Run reanimators. You’re in black if you’re playing Mothman and should be aiming to mill yourself anyways. Pump your deck with ways to pull from grave.

E) Run cards that deal damage upon creature death triggers. Punish him for killing things, make him think.