Was able to find a Frisk Pokemon (Trevenant4) in the Battle Tree in Ultra Sun and did some mock battles. Putting this comment so I don't forget. Here's what I have so far with the computer having a Frisk Pokemon:
1. For the type reducing Berries, this one depends on the Pokemon who has the type reducing berry. For example, vs a Rindo Berry Jellicent, Trevenant4(Which has Trick Room, Focus Blast, Shadow Ball, Energy Ball) will go for Shadow Ball. However, vs something like Rindo Berry Gastrodon, Trevenant4 will still go for Energy Ball since it is still its strongest attack vs Gastrodon, as the Tree AI tends to go for its most powerful move when attacking.
2. For Weakness Policy, the AI will not stay away from super effective moves, as Tree AI goes for its most powerful move vs a Pokemon when attacking.
Unfortunately, there aren't any Frisk Pokemon who have a move like Trick or Switcheroo, so this one I may need to get creative to figure this one out or find a Pokemon with Trick (like Reuniclus4) and hope the AI kind of just knows what item I am holding. I feel like that the AI doesn't need Frisk to confirm what item you have, as the AI seems to sort of know what item you have. For example, I did some mock battles with things like Kebia Berry Azumarill vs Venusaur, and Chople Berry Pangoro/Scrafty vs Chesnaught. For the Chople Berry one, Chesnaught would use Hammer Arm at first, but after exiting the battle and starting it over, Chesnaught would go for Wood Hammer instead of Hammer Arm. For Azumarill, Venusaur went for Energy Ball vs Kebia Berry Azumarill instead of Sludge Bomb, though this one was vs Red, so I wonder if Special Trainers have better AI that sense what item you have without using something like Frisk. :P
...Keep in mind this is for Gen 7. I can test for Gen 6 (and 8 if I get around to that and if I remember if Gen 8 can let you save battles to mock battle them), but only after I find a Pokemon with Frisk in the Battle Maison to mock battle there. Don't have Gen 5 or Gen 4 games, so I can't test those gens, someone who has those games would need to test.(Also they don't let you mock battle your Battle Replay xd, which is really useful to help test this out)
