The final boss of Super Mystery Dungeon! I had a hard time with this battle too.
Here are some tips:
-Stock up on Reviver Seeds. You can exchange 1 gold bar for 5 of them, I think. Bring as many as you can!
-Always use your Alliance moves. Spam them constantly, and drink Elixirs when you're low on PP.
-Wear any anklet that boosts your defense/attack or gives the opponent status conditions.
Hopefully this helps. ;u;