
This is one of those really cool trump-cards that may or may not blow a scenario out of the water. It's obviously more likely to pull its weight with more players and more pulls from the deck, but even in two player the card is warranted as a way to clear two or three foes at once.
A few factors in this card's great strength:
- You pick the target, obviously you pick the easiest one, this means you can hit a Ghoul Priest by targeting a Swarm of Rats.
- It's an extra 2 damage attack, when Shrivelling inevitably runs out you wont be dead in the water just yet. Also every additional target hit by the area effect is effectively a saved Shrivelling charge.
So, why then does not every deck have 2 copies? Because it's extremely expensive that's why! Obviously a card capable of hitting as many foes as Shrivelling has charges is going to be very expensive. Playing this card will prevent you from utilizing Arcane Studies, slow down the rate at which you play Spirit Athame, Holy Rosary, St. Hubert's Key and so on and on.
So, to play this card, make sure you're accounting for the cost, and if you can't then just leave it well enough alone. Also, avoid in solo, playing Storm of Spirits against a single target isnt terrible, but the severely reduced chance of multiple hits in solo reduces the value of this card drastically.