It’s just a shame about the Dark-pop in weakness.
To reach this point, you need tofocus on evolving Ralts on your Bench.
They should be evenly matched, buteverything in the Cresselia ex deck is weak to Darkness.
But even that might not save it, since Greninja can toss out a 20-damage Water Shuriken each turn.
This can be done quickly, sometimes before your opponent can get another Pokemon on the Bench.
Charizard ex / Moltres ex
Charizard exmight bethe worst possible matchup for Cresselia ex.
This is especially effective if your opponent has invested all of their Energy into a single Charizard ex.
Shock your opponent with Pokemon Pocket’s Darkrai ex/Magnezone deck.