Spectral Razor is great and provides exciting flexibility for Mystics who want to handle combat but don't want to stack up charge-based assets. My favorite experience so far has been running a single copy in Father Mateo as a tidy little insurance policy for when the Serpents of Yig eventually show up. And I built a Patrice Hathaway deck for a friend that included two copies of the whole cycle (this + Read the Signs & Ethereal Form).
There two major rules points that are important to playing this card correctly, and which sent me frantically googling the first time my group tried to resolve one.
First: the consequences of "add your value." As other reviewers highlight, Spectral Razor is different from many previous cards because it adds rather than replaces the base skill being tested. The most obvious effect is that you're able to get big fight values very easily -- adding and can get you to totals of 6, 7, or 8 very often. But it also changes how you can further boost that skill value. Specifically, you can't boost this attack with pips on committed cards (like Guts), because according to the) rules for skill checks, players can only commit "cards with an appropriate skill icon" which are "[ones] one that matches the skill being tested, or a wild icon," and doesn't match Fights. However, you can boost your with many actions like those on Arcane Studies. The timing) rules of skill checks give windows before and after committing cards in step ST.2, and the final value isn't calculated until ST.5, when you "apply all active modifiers" to the base skill...that's when you add your . And, as the FAQ to Lockpicks makes clear, there's nothing stopping you from boosting a skill other than the one technically being tested.
Second: interaction with Aloof. There seems to be significant disagreement about this in previous reviews, but as I read it, Spectral Razor can be used to attack and engage an unengaged Aloof enemy. The difference comes down to the difference between Fight, which is an Action Designator, and "attack" which describes a mechanical operation that is a part of the Fight Action, but can also be triggered in other ways (for instance, Enemies "attack" investigators without taking Fight Actions). In the rules) for Fight, it states: "An investigator may fight any enemy at his or her location..." and it is the specific) rules for Aloof that intercede: "An investigator cannot attack an aloof enemy while that enemy is not engaged with an investigator." The difference in wording between "fight" and "attack" in these two lines implies that one can trigger a Fight Action against an unengaged Aloof, but simply couldn't resolve the attack portion of the Fight Action. This is where Spectral Razor's wording comes into play, allowing the Fight Action to start and then engaging the enemy in question "immediately before" the rules would prevent the actual attack.
Rules questions aside, this card has over-performed for me, and is a great option for asset-averse builds!