Overpowered abilities, attacks, moves, perks, etc. that have made a game too easy

[Super_Boom]

Team/Partner Up in Fire Emblem Awakening - I try to avoid using it whenever possible, but sometimes it's necessary to keep a unit safe or transport them quickly. I prefer the Rescue mechanic of the previous games, which penalizes you for hiding units, rather than letting you create super-units that wreck everyone.

Multi-Strike+Pierce in SMT Devil Survivor - If your unit has high agility, you can basically kill most opponents in one turn with this combo. You can also add a skill to turn your enemy to Stone, which increases how overpowered this is even further. I feel like most SMT games I've tried have had a overpowered build towards the end of the game, but this is the one that comes to mind first.