The downside is that the card has a chance of dealing three damage to you on your upkeep, but this downside is far outweighed by the absolutely ludicrous upside
Some advice to potential Cube-builders: Although you don't want too have too many boring cards in there, you need to make some concessions to allowing a decent mana curve and having a sufficient number of creatures
(Oh, Kellan, I want to hug you, you sweet kid.) We can see the scene in the card Plan the Heist, when Oko relays his plan to the group: sneak into Tarnation disguised as Hellspurs and blend in long enough to get to the vault doors
Then Arceus VSTAR showed up and suddenly everyone was running decks that were Arceus VSTAR and so-and-so
[10] There are five types of cards split between the main deck or used elsewhere: [10] Main deck cards: Character represent your crew and have the color blue on the backs of the card Event one-time effects that are played from the hand Stage represent the location where the crew is played, often providing a benefit to your Leader of Character cards