Armed with foreknowledge of what the other Gym Trainers use, I'm better able to set up for each one's first Pokémon, which results in Biribiri being level 34 rather than level 33 entering the battle with Koga, and still having everyone else at the same levels they previously entered the battle at.
Luckily, the second attempt goes just as well as the first. Cody gets through the first two Venonat without even having a status effect inflicted once, albeit with more damage taken so I had to use a Lemonade. Hobo took a little longer to take down Venomoth, too, and took quite a bit of damage, but still pulled through. Now to see about acquiring that Slowpoke...
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I'm a cat person, but I can still appreciate a SuperNiceDog.