Two of its modes are two for ones and the steal ability has multiple relevant targets in Modern, so I would recommend playing this card in most decks which are able to pay for its restrictive mana cost
It's the kind of top curve that can certainly win the game, but not something you're always in the market for
Bequeathal Bequeathal is an insurance policy to put on your best threat, or slap it on an opponent's creature right before killing it
And then our spells cost one less for each one they share
Each of those, like the Darkness Crystal, will reduce the mana required to cast a spell in its appropriate color by 1, and will cost four mana two of the color of choice, but the rest is unique to each Crystal
Necropotence is black's best card-drawing effect, and thats precisely what combo decks are looking for