Magikoopa...
Oh, please! I wouldn't call this a battle...maybe a disagreement, or a nonverbal misunderstanding, if you will.  I guess Magikoopa was just too incredibly loyal underneath the mental block Smithy gave him to put some real effort into this one; either that, or he's really let himself go since the last time the two of you faced off. Take Bowser and Geno, have 'em wearing fire clothing and magical items such as Safety Rings and Badges, Jinx Belts, and Quartz Charms. Have Mario on at least level 20 with the Lazy Shell weapon, Bowser on level 20 as well with the Drill Claw or Spiked Link, and Geno on level 21 with a Star Gun or a Hand Cannon. 2 or 3 rounds should finish up this mixed-up mage. That is, if he doesn't summon clones like Jinx to do his dirty work.