Name: Riley Coyote
Age: 32
Species: Cartoon Coyote
Home Continuum: Looney Tunes
Department: Floaters
Partner: Rhodes Runner
Fandoms: Pirates of the Caribbean, Super Mario Bros., Looney Tunes, Harry Potter, Sherlock Holmes, The Chronicles of Narnia, etc.
Lust-Objects: No official ones, but he tends to act oddly around Anamaria from POTC.
Favorites: Wile E. Coyote (again, natch), Bowser, Jack Sparrow, formulating plans, things that go boom, etc.
Weapons: Explosives, traps, a cartoonish six-shooter (brand unidentifiable, but appears to be a .44)

Riley Coyote is a replacement of Wile E. Coyote from the same Looney Tunes AU as Rhodes Runner. His status as a character replacement first came under suspicion when he had failed to use a sign to communicate even once whenever he actually had some lines to say. It was confirmed by his disregarding Rhodes Runner when, and instead focusing his attentions on the "star" of the story, a Replacement!Sue impersonating Lola Bunny. His character was sufficiently complex enough to warrant rescuing, and he assisted the Agents, along with Rhodes, in killing the Sue and finding the real cartoon stars.
He is a bit more cynical than his partner Rhodes, but is overall a decent guy. He does retain the "mad scientist" traits of his canon counterpart, and is an ardent believer in the notion of applying explosives to any sort of problem, no matter how trivial. He gets slightly annoyed when he's in a continuum without explosions of some variety, and seriously annoyed when he's in a fic featuring any sort of uncanonical Bad Science (Biology, Physics, etc.). He also appreciates a person's ingenuity, tenacity and perseverance, so he gets REALLY irritated if a character disregards his dreams or goals because of a Sue's presence. Sometimes, he gets aggravated by Rhodes's antics, but usually he just takes it in stride (though not without being snarky about it).

Okay, that actually sounds pretty cool.

As for how much it should be toned down, my usual rule of thumb is that while in their home continuum and in HQ, an agent is able to behave normally, as per the rules of that continuum. However while in another 'verse with different rules, the agents are bound to follow those rules, at least as much as possible. So if Rhodes and Riley are visiting, say, Narnia, they won't be indestructible or be able to pull giant rockets out of nowhere. However, if they were visiting Tom and Jerry or Scooby Doo, or whatever, they'd have a lot more leeway with what they could do.

Of course, other people might have better suggestions for how to handle it.