-One of the boss fights in Castlevania: Dawn of Sorrow became very easy if you used a certain ability on some guy that mimics your ability, then attacked with only swords/axes/ etc.
-Same series, Portrait of Ruin, had a "doppelganger" boss that was easy if you didn't equip any weapons or abilities and went "mano a mano" so to speak.
-I remember the zombies in the first Resident Evil (PS version) would lunge at you at a 90 degree angle from where you were facing, so if you rotated then quickly turned another direction and ran they'd completely miss you. Also, the Hunters were easy to kill with a knife if you charged them and kept stabbing their feet. They'd block and growl, but couldn't attack because you'd hitstun them.