I know that SoW targets immortal, but the point of the card is that it targets immortal creatures - That's how it benefits the player more in an aether deck, which is the point of shards.
I don't think the point of this card is that it targets immortal, enchanted or sanctuary'd creatures/permanents/players. That sounds tacked on.
As for the card, I would recommend a cost reduction or even a
cost, to improve how easy it is to slot into a deck.
I could name quite a few uses for this card if it was a chroma cost, actually.