For me it was Noel,Aya,Samson and Titania
Noel because same reason as you, it seems like he can control the weather because every time i battle him it is fricking raining FINE if i cant set fire to the house then ill just spam sludge wave with Dragalge nyahaha!! ψ(`∇´)ψ
Aya : this is only because it was my first time and i underestimate her so i got curbstomp so bad a couple of times not to mention that field effect benefits her more than me as it nerfs most ground type attacks i found it easy if you let her Toxapex alive as it keep spamming toxic spikes
Samson : because of big top arena not only does it boost fighting moves depending on luck but my pokemon always got outspeed with Hawlucha with unburden which keep using arcobatics like OMG (╬▔皿▔)凸
Titania: F*ck you A-sandslash y r u so quick and spamming earthquakes not only that but the hail is annoying rendering focus stash useless not to mention the field changes fire type to dragon type i was so confused when my charizard use heat wave on that stupid Klefkie and the game said it does not effect it .AND that aegislash of hers FFFFUUU*kkk i cannot predict when will it use king shield so annoying (ノへ ̄、)