I really cant see this being worth more than a buck or two unless Nissa is in every green deck and they all want to play a mana ramp spell at 4 mana
You gain life equal to the damage prevented this way
Wrenn and Seven is tailor-made for decks that want to dump their libraries into their graveyards for nefarious purposes
Sorcery speed isn't perfect, but it's another way added to the very short list of ways to exile a creature with blue, and now you can hit artifacts too, something blue typically struggles with, so this is great
Boon of Safety | Illustration by Robin Olausson When a permanent with a shield counter on it (usually a creature) is dealt damage or destroyed, instead a shield counter is removed and that instance of damage/destruction is prevented
Its a great fit for decks that naturally mill, that fill their graveyard, or that revolve around delirium