Rival Eidolon/Summoner Ideas

So I'm working on a campaign where the players are all summoners (unchained spell list, can choose from either the APG or unchained eidolon), and while half of it is going to be a dungeon-crawler the other half is going to be fighting in an arena-type thing against other summoners for tournaments.

What are some of the eidolons you've seen in action, both APG and unchained? I'd love to hear any ideas you've had, to any degree of detail - I'm wanting things other than just my design philosophies to flesh out the stables of summoner/eidolon opponents. The weirder, the better, because I want the arena side of the game to be interesting enough to warrant devoting play-time to it and one of the best ways to do that is by trotting out strange and interesting opponents.

Pokemon.

Digimon.

Fate/Stay Night.

I don't want to tell you to steal ideas from these series steal ideas from these series but you can take some loose inspiration copy things wholecloth and put your own spin on them to make something fairly original smash all of them together into an unholy/un-axiomatic gestalt and fresh for your players, while still feeling familiar in some ways I ran out of Deadpool jokes to crib off of.

But more importantly, have fun with it.

Depending on what level, Gundolon.
Dash of Gunslinger, Synthesist archetype, ALL the arms.