I never saw Tirek break a sweat just eating. So Tirek Vampire Battle. Sorin Markov vs Dimitri Maximoff
Sorin, since his dramatic entrance was more impressive. All classic Cartoon Network / Nickelodian villains (Led by a significantly more intelligent Zim and Gaz) or all CN/Nick heroes led by Dib, Finn, and Jake?
That's a tough one, but I'd say the villains. The Lich alone could destroy half of the hero team. Tenchi Masaki vs Son Goku.
The Justice League. Superman alone could do the job, and when you add Batman, Wonder Woman, Hal Jordan, and the others, it ceases to be anything close to a fair fight. Bec Noir vs. Alucard.
Hmm, which Alucard? From Hellsing or Castlevania? Doesn't matter, Alucard all the way. Battle of the Sun Princess Celestia vs. Helios.
Ezio, his beard alone is enough to secure victory. Max Payne vs Detective John Hartigan in a gritty monologue face-off.