Its Mega Evolution introduced in Generation VI with Pokmon X and Y adds a competitive edge, making it a viable choice in battles due to its increased defensive capabilities and the addition of the powerful Magic Bounce ability
You can also cause your opponents to lose life or gain some life of your own with cards like Sheoldred, the Apocalypse and Starscream, Power Hungry
Its at its best in decks that care about a quantity of equipment, like Kellan, the Fae-Blooded
Level-Up cards must be played onto the corresponding Pokmon like evolution cards (though, in one rule change, it must be the active Pokmon), allowing for a variant of the Pokmon with greater HP, damage and additional attacks - as well as being able to use the moves of the card from which they levelled-up, unlike evolutions
It would be valuable even if it just got basic lands, but you can even set up Dark Depths, find Gaea's Cradle, and far more
It wont get as out of hand as Gisela Boorish, but itll still create a fair few tokens