There is an argument to be made about the Final Aeon possession also being part of this mechanic, but I am not really so sure
Well, because the card is a draw engine
The Darkness Crystal is fine and might actually be a funny sideboard card against the sacrifice decks because it turns off death triggers, but its usually not worth the mana investment
Phasing out also lets you use it effectively on your own creatures, as a protective measure for your opponents turns
That fact has rapidly catapulted Liberator, Urza's BattlethopterLiberator, Urza's Battlethopter to the number three spot among colorless commanders, with it sitting only 800 decks behind Traxos, Scourge of KroogTraxos, Scourge of Kroog
Slivers are beloved by their pilots and notorious to play against in the best possible way