@miketheprof Serenity has a couple major problems, the largest of which is that it blows up all your own artifact mana. The card isn't much of a 5 for 1 blowout when you are nuking 1 or more of your own moxes. Additionally, Serenity is incredibly slow. The current iteration of Shops kills so quickly that a 1 turn delay may give the Shops player enough time to kill you, or else set up Ravager+Factory. A 6+ power creature immune from sorcery speed interaction is surprisingly tough for many decks to beat.
Lastly, when comparing Serenity to other hate cards, it is somewhat similar to Hurkyl's Recall in that it gives you 1 turn to do whatever broken thing you want unencumbered by taxing effects or graveyard hate. There are very very few decks that need a 1 turn window to go off that simultaneously do not need a large base of artifact mana or a key enchantment in play. The only current viable deck that can play it effectively is Dredge or a blue control deck, and the control decks already have effective hate in Ancient Grudge and By Force.