Gohan & Cooler (Dragonball) vs Percy Jackson & Luke (Percy Jackson) - strongly resisting the urge to vote agains DB out of spite...
Drizz’t & Mina (Dungeons and Dragons) vs V & Xykon (Order of the Stick) -- Sadly, based on Forum Explorer's description, Mina outclasses the hometown favourites. I think it will be a good fight, but ultimately a loss for Ears and the lich.
Fighter & Black mage (8 bit theatre) vs Luffy & Crocodile (One Piece) -- pass
Lucy & Hades (Fairy Tail) vs Saber & Berserker (Nasuverse (Fate/stay night)) -- pass
Beowulf & Basilisk (Fairytales and Folklore) vs 4th Hokage & Orochimaru (Naruto) -- I'm assuming we have a rather large serpent-type basilisk with stone-gaze. I don't know much about Naruto, but Beowulf is superhuman and has a statue-making friend.
Sora & Sephiroth (Final Fantasy) vs Rainbow Dash & Nightmare Moon (My Little Pony: Friendship is Magic) - as mentioned, FF power levels are screwy, especially when comparing storyline to in-game abilities. I think this is probably the most unpredictable fight, but I just can't vote for those weird little ponies.
Freddy Kruger & Jason Vorhees vs Sub Zero & Reptile (Mortal Kombat) -- Horror movie villains are notoriously difficult to kill, but this isn't necessarily to the death. The Mortal Kombat crew can out-maneuver F and J and most likely incapacitate them.
Edward Elric & Scar (Full Metal Alchemist) vs Samus & Dark Samus (Metroid) -- speaking of out-maneuvering, I think Samus and her dark twin have the edge here: high mobility combined with massive firepower.