OVERPOWERED:
From Demon's Souls we have the Mirdan Hammer which does very high damage when upgraded, attacks very quickly, has a very long range, and can destroy blockers. Though Northern Regalia has quite a bit higher damage, the Hammer is much faster and longer range. Doesn't help that 1 setup gives it HP regen. Combine that, with the HP regen shield and the regen ring to have a very cheap setup.
Gundam in Gundam: Crossfire is ubertastic. Though late in the game very expensive, tis neigh-indestructible. I have it maxed and 2 others maxed for my allies and nothing stands a chance. Even the final level on the hardest difficulty was a cake-walk. Normally your allies last half as long as a doughnut in a police station, but even they can't die when piloting Gundam.
Urban Cohorts in Rome: Total War. Fairly quick, they have a very powerful ranged attack (though only 2 volleys), very high armor, and will defeat ANY other infantry head-on (even if you run headlong into the speartips of a Spartan phalanx assuming you hit the Spartans with the javelins).They are also a LOT cheaper than the only infantry that can stand up to them. Praetorian Cavalry also get mentioned for being able to best even Cataphracts (normally the best heavy horsemen in the game). All online Roman players LOVE both Praetorian Cav and Urbs.
Snake in SSBB has quick attacks, oddly large range, and high damage and knockback. His basic combo can often KO middle weights at 60%. He is mostly unmatched in ranged warfare and is a beast in melee. He can move fairly quickly and has great recovery. MetaKnight is said to be the most unbalanced, but he never fairs well in my Smash group. Another special mention to Pikachu's Down special, the thunder of uber cheapness and G&W's hammer.
