[Intense Mode] Marianette Gym Guide - Pokemon Rejuvenation
6See Full Series here: https://www.youtube.com/playlist?list=PLezAEu8shuO6qdBP5Qq_wjqRpDHhtOSDT
This is a Gym Leader episode where Metro describes exactly how he beats Marianette.
If you want to see the attempt where he wins, skip ahead to 13:25
The basic strategy goes like this -
Any Poison type against fairy, only need to win the battle with one pokemon.
Swellow comes out second as long as poison type is also bug. Send out any good rock pokemon and chip away.
Cinccino with Skill Link comes out, so you either need to always hit first or survive one round. High Jump Kick seems mandatory.
Ambipom is similar but isn't as fast so you should be able to find a way to 1 shot it with a High Jump Kick.
Slaking will actually not do a single point of damage most times, provided you can kill him quickly. Set the condition elsewhere and just trust the RNG here.
Pyroar is also hardly a threat unless you get unlucky with Swagger.
Should be a near 100 percent win condition if the Slaking cooperates.