No I don't mean Pokemon yet you can post it if you want. By rival I mean how some rpg's has a battle between you and a group on people or one person. Like in Tales of the abyss you fight Asch, Tales of vesperia you fight Flynn, In sonic adventure battle 2 you fight shadow. Like that of course my favorite would have to be

*spoilers for tales of xillia* 

 

Alvin that battle between Jude and Alvin was amazing not the battle itself just the hype living up to it.

Tales of the abyss: Asch meaning of birth made that battle the way it is *REPLICAAAAAAAA

Naruto ultimate ninja storm 3: Yes the Naruto vs Sasuke boss battle was quite good which is why I love it so much (I know that didn't make sense but I can't explain it.)

 

Fool. Dante vs. Vergil in Devil May Cry 3.

Ventus VS Vanitas.

Sonic vs Metal Sonic

Lucas vs claus

 

I can't remember much besides that 

Green (Blue in the English release, I find his JP name more fitting though) from Pokemon Red/Blue/Green/Yellow/FireRed/LeafGreen

Silver from Pokemon Silver/Gold/Crystal/HeartGold/Soulsilver

Hugh from Pokemon Black 2 and White 2

Though I have yet to encounter him in his original game, Gilgamesh from FF, namely FFV.

Goku vs Vegeta in every DBZ game.

Sora vs. Riku

Link vs. Ganondorf

Red vs. Blue (Pokemon)

Cloud vs. Sephiroth