This ability is pretty good in its own right, as moving a counter to a creature that is best at using it can allow your turns to go much more smoothly
Mew ex isnt without its problems While this new card is sure to topple the current meta and is likely to become an S-tier option, it does have its failings
Decks will be non-MTGO decks that placed at in-person events like Pro Tours, GPs, State Champs, etc
You could even use a card to find target creature in your library and get a forest if you wanted to with natures revolt in play
-And of course the ACE SPEC Sparkling Crystal (that makes the attack cost 1 less energy)
----- Flying Super Nova As this creature transforms into Sephiroth, One-Winged Angel, you get an emblem with "Whenever a creature dies, target opponent loses 1 life and you gain 1 life." Whenever Sephiroth attacks, you may sacrifice any number of other creatures