Gohan & Cooler (Dragonball) vs Percy Jackson & Luke (Percy Jackson) - No contest.
Drizz’t & Mina (Dungeons and Dragons) vs V & Xykon (Order of the Stick) - Pass for now, I don't know who mina is. However, if they're not significantly more powerful than drizzt, I'd give this to OOTS purely because xykon appears to be higher level (and is a spellcaster).
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 going to go out on a bit of a limb here and assume that the 4th, given that he's kakashi's teacher, would probably do a similar sort of thing and use kage bunshin to gather information when fighting an unknown opponent. He can then find out the basilisk's power and stomp it while blindfolded or something, or just overwhelm it with clones. Beowulf is probably a non-issue compared to the ninjas.
Sora & Sephiroth (Final Fantasy) vs Rainbow Dash & Nightmare Moon (My Little Pony: Friendship is Magic) - Nothing can destroy friendship, it's the most powerful force in the universe! It's even stronger than chuck norris!
Freddy Kruger & Jason Vorhees vs Sub Zero & Reptile (Mortal Kombat)
Edward Elric & Scar (Full Metal Alchemist) vs Samus & Dark Samus (Metroid) - I like FMA, but I doubt alchemy is going to work very well against metroid tech.