mtg black energy cards Darkness | Diamond & Pearl—Majestic Dawn Return Cthonian Nightmare to its owners hand Best Energy cards to pick

Opposition is a card that you might want to pair with another color that produces tokens for its full value, but this is just broken

It's got First Strike and Protection from Red for some reason, and apparently those nasty Sea Trolls hunt the Narwhals

Its basically a one-mana Cryptic Command, and that comparison should show you why this is one of the best Modern sideboard cards

Plague Rats, most obviously, is non-functional in a context of 60 card minimums and 4 per card maximums, but is hilarious and brutal in a 40 card minimum environment where an opponent may have a dozen or so Rats

There are no rules here so long as the cards in question are legal for your format