Koga rechallenge is practically impossible if you can't knock him out quickly.
I can't recall what happened anymore, but I didn't knock out his Muk immediately.
Bad mistake.
His Muk's moveset is Minimize, Toxic, Swagger, Screech. He poisons you, spams Screech, uses Swagger, then proceeds to Minimize until you're not confused anymore, at which point he confuses you again with Swagger and returns to Minimizing. With your defense at minimum and your attack at maximum, you will all but OHKO yourself with confusion damage. Even when you CAN break through confusion, 90% of the time you'll miss.
I finally beat his Muk and then his weakened Venomoth (he had Baton Passed it out to Muk earlier) took me out. I had many more revives and potions to use but I didn't feel like wasting them if I clearly wasn't ready for the E4 rechallenge, and I'm clearly not.
So. Training against the E4 is clearly a bad idea at this point. I'll have to settle for the uncooperative Gym Leaders. (Apparently, Brock thinks that evening starts at 8 o' clock.)