I also think that an interesting direction would be to add a variety of tempo-prison style cards to the deck to slow down the speed under which people could play cards
This particular one is entirely distinct from the others, being part of the rare group of Shining Pokmon cards
Im personally not a big fan of this for Commander because it incentivizes players to bring their mana curves lower and lower, which makes Commander feel closer and closer to competitive Magic play, when the format was birthed as an alternative to that style of Magic where big, splashy spells could have a home
Someone is creating a board of destruction, you drop this, and they go back to nothing
If you're playing a deck that floods the board with creatures, then you can simply make sure everyone else loses their creature and you get to keep yours
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