It curves perfectly with a turn 1 Aether Vial, letting you Vial it onto the battlefield and immediately crack the Clue, using your Vial activation and all your mana on turn 2
Double the damage, double the fun
Notably, this means that if Space Beleren's +1 ability has been activated earlier in the turn, creatures are no longer restricted from blocking, so watch out
Elves can struggle in formats with interaction that stops them early, usually a cheap sweeper
The mana effect was the one that counted, and there were a lot of good reasons to want to play a deck based around it
Gameplay-wise, Shadowy Concealment makes Mega Gengar ex fun to play with, too, as it reduces the Prize cards opponents take when one of your Darkness Pokmon falls to a Pokmon ex subtly altering prize trades