Mario Rap Battle Ideas:
Mario vs. Bowser
Mario vs. Princess Peach
Mario & Luigi vs. Wario & Waluigi
Mario & Luigi vs. SpongeBob and Patrick
Mario & Sonic vs. Bowser and Dr. German
Rap Battle of the Marios: Mario vs. Dr. Mario vs. Baby Mario vs. Paper Mario
Paper Mario vs. Toon Link
Baby Mario vs. Young Link
Mario vs. Pikachu
Mario vs. Sonic 2 (Fire Mario vs. Super Sonic)
Mario vs. Luigi 2 (Fire Mario vs. Ice Luigi)
Mario vs. Link 2 (Fire Mario vs. Fierce Deity Link)
I meant to write "Dr. Eggman."
Mario Rap Battle Ideas:
Mario vs. Bowser
Mario vs. Princess Peach
Mario & Luigi vs. Wario & Waluigi
Mario & Luigi vs. SpongeBob and Patrick
Mario & Sonic vs. Bowser and Dr. German
Rap Battle of the Marios: Mario vs. Dr. Mario vs. Baby Mario vs. Paper Mario
Paper Mario vs. Toon Link
Baby Mario vs. Young Link
Mario vs. Pikachu
Mario vs. Sonic 2 (Fire Mario vs. Super Sonic)
Mario vs. Luigi 2 (Fire Mario vs. Ice Luigi)
Mario vs. Link 2 (Fire Mario vs. Fierce Deity Link)
Source Rap Battle.
Mario's Princess Peach vs Sonic's Princess Sally Acorn
And maybe X-Men's Rogue vs Sega's Bunnie Rabbot(battle of the Southern Belles)