I shouldn't have to say this, but SPOILERS! If you don't want the game's ending spoiled for you, do not watch this video.
If you're looking for a strategy for the final boss, all you need to do is survive. Be prepared with appropriate items to restore HP and/or PP. If you've gotten to this point, you really shouldn't have any trouble with this fight. Keep your HP high so that you have plenty of time to heal if you get hit with a powerful attack.
Mother 3 for GameBoy Advance with English patch.
Developed by Nintendo, Brownie Brown and HAL Laboratory. Written by Shigesato Itoi.
English patch can be found here: http://mother3.fobby.net/
Please support the Mother series by purchasing official merchandise.