These are some designs that I made some long time ago and lost, so I had to redo them from memory, I think they ended up looking better than the original
The idea was to make characters that were not necessarily villains but more antagonists or rivals for the loonatics, even potential members of the team, not all of them would have powers, some would require their physical abilities and technology.
Tory Russo could easily be an old friend of Lexy's who got superpowers and has a hard time controlling them (cryomancer) , she could also be a love interest for Duck,
Pierre le pew would have some smell that influences people's emotions (perhaps a colony), and would be a good swordsman to rival Ace
Peeny Pussycat (shadow cat) would be a professional thief who has a avanced tec suit that makes her invisible, she plays for her own side and can be both an ally and an enemy.
Fox is perhaps the most original for not having a better-known counterpart to the Looney Tunes. I imagine her as a hacker, an expert in clandestine weapon technologies and a potential rival for tech.
Finally Veloz Gonzales and Toro would be sporting rivals for Rev and Slam respectively, although honorable rivals, Veloz would have superspeed and Toro super strength and invulnerability