In that field Sludge Wave does additional Water type damage, hence why it's super effective against a Charizard but not against Noivern. For me I beat it with my prankster Whimsicott Stun Spore, then it got paralyze hax so I could add a Leech Seed, Whimsicott went down, then I deducted it would probably be poison water like it's surroundings so Galvantula with Electroball managed to take it out quite fast, of course with a added damage because the surrounding water conducting the electricity.
It was quite easy.
On topic of the difficulty of other PULSE mons,
Avalugg was quite easy because Houndoom + Flamethrower(even PULSE Ava don't like no special moves)
The Tangrowths were harder but if you managed to use Poison Spikes before they switch in, like with the last 2 it gets easier. PULSE Muk was quite hard because I didn't have any good mons on me, pulse Abra was the hardest because of the level gap imo..
But we still have the Clawitzer and Mime and whatever is in Agate to deal with, so...