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>Type
Poison-type
>First Team
Arbok
Nidorino
Haunter
>Rematch team
Arbok
Crobat
Nidoking
Venusaur
Tentacruel
Gengar
>Aesthetics
The gym is a front for Team Rocket, to test trainers to screen potential recruits.
The gym itself is on the upper-floor of a shipping factory. You can see crates, trucks and people below working away (transporting stolen goods and such to Rocket laboratories).
First run of the gym has the trainers there as workers and overseers, second run they drop the pretense and adorn Rocket uniforms.
If you choose to join Team Rocket after the second battle you can buy pokemon from previous generations here, and they have a fully stocked store, a poke center, and a pokemon breeding facility in the back rooms. If you choose to turn them over to the cops you get the same things but not run by the Rockets.