I completely forgot to answer this but here it is (a week late)
This is my personal strategy, and it works for me.
Try using a non-evolving mon such as:
Latias Suicune Darkrai Ho-Oh Zacian Comfey Mew Buzzwole Hoopa Absol
Get damaged enough:
Try to:
A) Act AFK until you get beat up (more useful if your UNITE move is available and you have a way to quickly knock them out.
B) Try to follow a teammate around, but not too closely so if you see an enemy, they can initiate combat, and you just sit there and take damage while they do the work.
C) Look specifically for people playing as Blaziken, Blissey, Darkrai, and Mew, as they are uncommon, but some of if not the best playable mons in Unite.
wait until the last minute of the match and wait for the inevitable storm on the enemy team if you are winning, or the storm on you if you are losing. Then unleash your unite move. and absolutely destroy 2 opponents.
Emote in the last few seconds to rub in your win (or your two KO's if you lost)
Rinse and repeat if you don't get it. There's probably better strats, but this is mine.
Hope this can help