One of the newest things that you should familierize yourself with is Pokemon Lv. X. They are unique forms of Pokemon that are used to upgrade you're normal Pokemon. Here are rules you should know about Pokemon Lv. X
1. They cannot be played as Basic Pokemon. You must put a Lv. X card on top of another card in the manner of of evolving it. For example, Put Dialga Lv. X on top of Dialga to level it up.
2. You cannot evolve Pokemon into Lv. X cards. For example, Grotle cannot be evolved into Torterra Lv. X. It must be evolved into Torterra and then leveled up into Torterra lv. X.
3. Pokemon cannot be leveled up on your first turn or on any turn you just evolved the Pokemon you widh to level up.
4. While in Lv. X form, Pokemon can use any attacks, Poke Bodies, and Poke Powers from they're previous form. For example, Palkia Lv. X can use attacks from the Palkia card and the Palkia Lv. X card.
5. Pokemon Lv. X count toward the four-card limit of a Pokemon. For example, you cannot have four Torterra and one Torterra Lv. X.
Hope I've been helpful.