Also, a very useful thing to remember is that the AI will NEVER switch a Pokemon (unless an effect forces them to). This is particularly useful against Kendall (who you face 4x in total), as when she has Dedenne in play you can just switch to a Pokemon holding 0 energy and watch as Kendall's unable to do anything and just decks herself out. But also against others it's a very useful thing to know you don't need to be afraid of a switch.
Unless they have a Switch or Escape rope card or another Trainer. But yes, they never (manually) Retreat.
AI trainers use all their resources, always. Even if it's the worst play ever. Sycamore the hand with 3 card in draw pile? They do to auto-deck out.
They will always add an energy, even to pokémon are going to be KOed this turn.
They will always use their items/tools, even in useless pokémon or almost KOed ones.
They will always play a supporter, if in hand.
They will always use their abilities, even switching a set up pokémon and promoting a weak with no energies one or leaving the pokémon without energies to attack (if the ability heals them or poison you, or whatever)
But still knowing everything and being experienced, there are Theme decks that are so slow and weak that can't beat Zack, or other trainers. Mainly HGSS and some of the B/W ones (Plasma Genesect deck is a pain for example).
But anyway, one way or another, you should be able to beat the AI trainers with the starter decks, at least in Gold league.
Try to promote active any pokémon that can last a couple turns and keep a powerful one in bench. Set up the powerful one and leave the other be KOed. Go on with all the power of the new one. That can work sometimes.
The other option is keep trying, once and again, until Zach just have so bad hand that plays only 1 pokémon and nothing in bench and you KO it before he can add anything to bench. And if he can, probably can stand behind you through the whole game not able to set up properly nothing else for a win.
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