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
Both of these creatures are brand new to Magic and both boast powerful abilities
Monsters: Desperado Barrel Dragon It's most of the times the strongest monster to play, and it can be special summoned in three different ways, -with heavy metal raiders if a dark machine monster destroys a monster by battle or a card by it's effect, -with it's own effect if a dark machine gets destroyed by battle or by a card effect, BM-4 Blast Spider can trigger this effect by itself, but it won't work with 'tribute' or 'discard' effects
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
They certainly work well together by giving you the ability to play Welcoming Vampire and another creature in the same turn earlier than usual