Any cards that Create lots of Tokens at a time can be extremely deadly for your opponents
Aang is the best example of this progression
The ability makes it tough to use unless youre running a full Rocket build, but once it's active, Erasure Ball gives you some serious power
Crown Rares are some of the rarest cards, featuring EX versions of the Booster Pack cover Pokmon in fill art, CGI effects, and a special gold spiral background
Vega, the Watcher can also get you some added card draw
(Some abilities can also target unexerted cards.) But not using them has less of a direct benefit - you dont need to defend your life points, as in MTG or Yu-Gi-Oh!, so leaving cards upright is typically only worthwhile if theyre likely to be challenged by your opponent and you need them for a future turn