Senator Armstrong and Desperado, the Patriots and Revolver Ocelot, Raul Menendez, Jonathan Irons (although i haven't seen AW yet), Shōgo Makishima also sounds interesting, MCU Hydra, maybe the Lich from Adventure Time, etc.
He should do Lennart Bedrager from South Park, Mrs. Trunchbull from Matilda (if he hasn't already), SMG3 from SMG4 (if he does ones on fan-works), & Tord from Eddsworld,