A combat version of Read the Signs, and I must say, I am quite stoked about this card. It's a problem solver. In mystics and other investigators that use their to do their fighting, Shrivelling charges are an important resource and you want to conserve them if at all possible. In those decks, this card is very powerful. It does 3 damage to non-elite enemies, and, as of this writing, this one shots more enemies than it doesn't. Also, the fact that Spectral Razor adds to rather than simply replacing leads to some very high number. Akachi Onyele attacks with a skill value of 8 using this card, and Jim Culver and Agnes Baker both swing in at a 7, and this is before any buffs from things like Holy Rosary or St. Hubert's Key.
The other benefit, that Spectral Razor automatically engages the enemy, is kinda niche, but it can be used to pull a boss monster off of one of your fellow investigators without using an action. At the very least, it makes sure you won't accidentally hit your friend in the face for 3 damage if you happen to pull the .
It is also missing the clause on a lot of mystic cards that makes something bad happen if you pull a special token.
As for its downsides, Spectral Razor is only single use and it costs resources to use. Mystic's economies often have a lot of demands placed on them, so trading one card for one kill might not be a wise investment.
The other investigator I was really hyped about using this card is was Zoey Samaras, because this is everything she wants. With her 4 and 4, Zoey would be attacking at 8 with this card. It does a bunch of damage, which is always good, and the free engage combined with Zoey's passive would give me back one of the resources I used to play this card. The only downside (and it's a big one) is that Zoey only has 5 out-of-class slots, and in faction cards do most of this quite well.