You could theoretically play it, then retreat your active Pokmon and attack
Graveyard Trespasser's primary utility comes in the form of graveyard hate, exiling a card from an opponent's graveyard whenever it enters the battlefield or attacks, draining that card's owner for one life if it's a creature
Najeela, the Blade-Blossom takes a more hands-on approach to its token generation, allowing you to create 1/1 Warriors each time a Warrior attacks
In situations like this, there is a much better chance of being able to correctly guess which cards the opponent is holding
For context, Mega Charizard Y ex's attack is powerful enough to wipe out almost every card in the game for the small sacrifice of 50 HP, and the only cards truly capable of countering the fiery icon are from the same new set
Pokmon details: Charizard, a Fire/Flying-type Pokmon, evolves from Charmeleon and is the final form of Charmander