Poison-Type Gym Leader
5th Gym
Badge: Secretion Badge
The gym would have an outdoor section consisting of a little nature preserve with a handful of different habitat types. For the puzzle, challengers would be given a specialized application to record data (mechanically, this would be achieved as a sub-mode of the Pokédex) and sent out to observe nine Poison-type Pokémon in their natural habitats.
Upon interacting with a given Pokémon, a unique bit of text would be added to the application, like an extra Pokédex entry. These Pokémon would basically be distributed in three sets of three, and accessing the areas where the latter two sets are would require defeating two gym trainers who are also conducting field work.
After obtaining data on all nine and returning to the start of the area, challengers would be given a three-question multiple choice quiz (basically asking them to choose the Pokémon which matches the snippet of information provided). An incorrect answer would result in having to battle a gym trainer (for a total of 2-5 gym trainer battles through the whole experience).
Upon completing the quiz, the battle against the Gym Leader would commence.
Following the model of four Pokémon (BSTs of one with high 300s, two with low-to-mid 400s, and an ace with high 400s to about 500) seen with Gen III Sabrina and Emerald Norman:
Clodsire [430]
Ability: Water Absorb
-Toxic Spikes
-Poison Tail [Poison Jab in rematches]
-Stomping Tantrum
-Slam [Megahorn in rematches]
-Dustox [385]
-Ability: Shield Dust
-Venoshock
-Bug Bite [Bug Buzz in rematches]
-Whirlwind
-Moonlight
Hisuian Qwilfish [440]
Ability: Swift Swim
-Barb Barrage
-Bite [Crunch in rematches]
-Rain Dance
-Waterfall
-Galarian Slowking [490]
-Ability: Own Tempo
-Sludge Bomb
-Eerie Spell
-Disable [Slack Off in rematches]
-Toxic
I could think up dialogue and additional rematch party members, I suppose, but perhaps I'll come back for that later.