Besides the ones that appear in the Super Smash Bros. games.
I'm thinking Master Chief calling in a MAC round; or Commander Shepard calling in the Mako or Hammerhead.
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Trevor Phillips ("High as a Kite"): Pours gasoline into an empty can, inhales the fumes, pulls out a grenade launcher, and raises hell. Big Daddy ("Rawr!"): Charges forward until it latches onto an enemy and inflicts massive amounts of damage. Damon Baird ("How Many Geniuses Do You See?"): Calls in a turret-mounted Silverback that's immune to damage.