It's fairly easy to get an 80% win rate on King Elmer if you use the right deck. It's mostly just about baiting him into using the cards you want in the right place.

For example I always open against him with Couerl in the top right corner. He will nearly always counter that by placing Godbert right beneath it. From there if you place your own Godbert card diagonally from it in the bottom-mid position you set yourself up for a plus finisher later on in the game. I use Sabotender to trigger the combo because you can place it in either of the two slots between the Godbert cards to trigger the combo (so it's very unlikely the AI will take both of those positions, especially if you distract him by playing a few other cards on the other side of the board). Just make sure to fill the rest of the board first before you drop that Sabo card and try to set up a combo chain (I often use Moogle in the top-mid position because he's weak on the right and strong on the left which combos well from the Couerl).

Thanks for this guide though, I still haven't challenged many NPCs outside of the saucer yet.