It puts your whole hand in your graveyard, which of course is useful for decks that want things there, and interacting with your graveyard is something that black naturally does quite well
Mardu colors give you access to all the top removal cards, and best of all, Edgar's eminence ability makes him useful from the command zone, where he can churn out mini-mes in safety
As a spell or ability tries to resolve, if all its targets are illegal, that spell or ability doesn't resolve and none of its effects happen, including effects unrelated to the target
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The caveat of all three types of energy needing to be different also makes it trickier to use, however, as some of the metagame's most powerful current combinations only utilise a couple of types, such as Duraludon VMAX decks that only use Dragon- and Steel-types Pokemon