Misty Terrain is working incorrectly, grounded pokemon can be inflicted with bad condition status by a non grounded pokemon, for example gliscor can toxic tapu fini, and non grounded pokemon cant be inflicted with bad status condition by a grounded pokemon, for example toxapex cant toxic gyarados.

Hey there, I was able to re-create your issue, I will mark it as awaiting internal tracker!

Hey there! We're currently working through old tickets, and upon testing this ticket, it seems that Misty Terrain seems to be working only partially correctly now- as of version 8.3.6, grounded pkmn (such as toxapex) can inflict ailments (such as poison) on flying pkmn (such as wingull or gyarados), as is expected. Flying pkmn can inflict ailments on other flying pkmn, which is also as expected. Grounded pkmn cannot inflict ailments upon other grounded pkmn, which is also as expected.

However, flying pkmn can also inflict ailments upon grounded pkmn, which is NOT as expected. Grounded pkmn should not be afflicted with ailments such as poison.

As such, I will move this ticket to internal. Thank you, and sorry for the delay!

Can you give the testing scenario you used to test this, @Katzyn?
What Pokemon were battling? What status moves?

Sorry about that!

I used mainly 4 pokemon, and did the following battles, using poison (Toxic, 90% accuracy) as my ailment, with the following results:
1) Gliscor (flying) x Tapufini (grounded) = Tapufini with Misty Surge could be easily and consistently poisoned via Gliscor's Toxic while Misty Terrain was active. (Misty Terrain should be preventing grounded pkmn from being affected by ailments such as poison.)
2) Gliscor (flying) x Gyarados (flying) = Gyarados could be easily poisoned, but this is normal, as both are flying, and not affected by Misty Terrain.
3) Toxapex (grounded) x Tapufini (grounded) = Tapufini could NOT be poisoned while Misty Terrain was active, which is normal, as both pkmn should be affected by Misty Terrain, and protected from poison. Could be easily poisoned AFTER Misty Terrain dropped off.
4) Toxapex (grounded) x Gyarados (flying) = Gyarados could be easily poisoned, which is correct, as Gyarados would not be affected by Misty Terrain, and therefore would not be protected from poison.