Fluxfire Feline. I doubt anyone has leveled one of these to 25 yet, considering the current XP situation. However it's easy to calculate his damage output so I figured we could start discussing it now.
There's two breeds, 5 and 8, with 293 power and 322 power. Let's just talk about the breed 5, since 293 power is more than enough.
If he uses Wind-Up, then Supercharge, then Wind-Up, he does (45+(2.25*293))*1.1*2.5 = 1936 damage. This is a lot! I was going to type out the calculation for the 322 power breed, but it's kind of pointless since 1936 one-shots virtually anything anyway. For reference, the du jour 3 turn combo of Lift-Off+Ghostly Bite (breed 7 Blighthawk) does 1381 damage (but with a 20% miss chance on the Lift-Off).
Some things to note: Supercharge does not have a duration, it simply stays on until you use an attack. This means that the Feline can choose to pass if the opponent uses Dodge/Burrow/Lift-Off/etc., and hit for the same damage one turn later. If you stun the Feline, he just waits until un-stunned and hits for the same damage one turn later. The breed 5 Feline also has 325 speed, meaning he will most likely be going first and will know whether the attack will land when he decides to use it. So you can delay the 1936 Wind-Up, but you probably can't make him waste it. This also means that you will likely only get 2 actions before getting hit for 1936. Finally, he's a mechanical: even if you kill him, he gets at least one extra turn to land the combo.
The solutions that I see are: kill it in 2 turns (this includes his rez, so it's really kill it on turn 1, then kill it again on turn 2; or you can take up to 3 turns if you can beat 325 speed); beat 325 speed and have an evasion or interrupt, and correctly guess when to use it; guess correctly with Reflect; be an elemental, in which case you only take 1290 from the combo.