Man, it would be sweet if you included MechaGodzilla and MechaKing Ghidorah at the climax, it would be like....
Mario: This robot lizrad will smah you!
Kirby: My 3-headed cyborg dragon can smolder you!!!!!
Both: Hyper Beams, GOOOOOOOOOO!!!!
Thats just an example if they duked it out in robo-kaiju at the end of the story........