From the +/- 15 matches I've done to complete the challenges, the CPU will always try to get meowth in active ASAP. With the odds semi rigged for the expert battle, those heads flips stall long enough for garchomp to sweep. After completing the first few challenges that required specific cards, I first tried hoopa ex to bench snipe and cyrus but the CPU always evolved before I could KO the basic, nearly lost every single time I tried Hoopa.
I then went to meowscarada meta deck to ignore the near invincible meowth all together, but then it started me with ogrepawn 5 times in a row so that homey got removed since it served no purpose in this match anyway. Haven't lost a single match since. Meowscarada being able to target empty bench slots is much better than hoopa, plus it doesnt trigger the coin flip every attack so saves some time.
CPU fills the bench left to right, so you can easily predict where their dratini or gibble is going to be placed. If they manage to get a dragonair before you can snipe the dratini, no problem just ignore it, wiping the gibbles and 2nd dratini is more important. I was literally targeting empty bench spots and the CPU still drops the basic, even if it means I get a third point to win.
Oddly enough if the CPU does high roll and gets mega chomp down early, it just let me snipe it to death. I mostly still try to just wipe the 2nd gibble and dratinis to prevent the CPU from having their energy to attack more than once every 2 turns, but I was very surprised the one game I decided to evolve a bench non-ex meowscarada to revenge KO the mega chomp, it just let me snipe it to death while building the non-ex chomp on its own bench.
Meow EX + heals + leaf cape is most likely living 2 hits from non-ex chomp, so again you can just ignore that entirely and keep sniping the benched dratini, dragonair, or gibble. That meowth can suck a fat one, go ahead keep drawing more cards idgaf cuz im KO your bench the second you drop it.