Every energy card you have in your deck gets that much better for every other energy card in your deck, and suddenly you find somewhere between twelve and sixteen spell slots already spoken for
This new creature has the colors, name, types and power/toughness of the card you put on top of the pile, and the combined abilities of ALL creature cards in the pile including any other mutators you add to it later
There are a couple of different versions to be collected, including a Secret Rare card with rainbow coloring, though this card is even harder to find than the Friends in Galar Trainer card
As with other Secret Lair releases, the DnD drops do have a limited quantity, so if you are interested youll be probably want to snag them quickly before they sell out as the cards often spike significantly in value on the secondary market and on eBay
Since you get to choose what card you discard, you can get rid of a GX or EX Pokemon in your hand, so there's no risk of it getting knocked out on the Bench, and Mewtwo and Mew-GX can take advantage of its attacks