Fast, 0 resource, Cancel a treachery card, costs only 1 xp.

Wow what a great card for seekers. The drawback is small(let's say it cost you 1 action to investigate).Even Roland can make a great use of it since he can add clues while slaying some monsters.

Like ward of protection and test of Will this card is an auto-include to avoid the terrible things that Mythos offers you and most of times punishes you.

Situational card just like Barricade. Can be used when you are preparing for a boss fight but other than that i can't see any play. Bad card for Solo since you need to move fast from location to another most of times. Can be utilized in O'toole decks with sneak attack combo for a total 4 dmg without even fight (let's add a dynamite blast there going up to 7). Other than that Harrigan and Yorick have better options for 1xp than this one.

Investigators who have problem with resources can make a use of it in a multiplayer game. Roland or Harrigan can put it in a 0 xp deck when they start a campaign. Τhe thing is that you dont want to be overwhelmed by enemies so usually the maximum will be +1+2 for the attack. Don't get me wrong but you want to deal with the enemy as fast as you so the Knife from core is better option than this one with the discard option.

This is a very strong spell for mystics in multiplayer games and the more people you are playing with, the stronger it becomes. It is similar to Dynamite Blast except that it only deals 2 damage and requires you to succeed at a Fight test, though you can choose the weakest enemy at your location to fight. Those drawbacks are balanced out by the fact that it costs 2 less resources and is in a class that is substantially more likely to have spare resources to play it. Additionally, it synergizes with other popular mystic cards such as Arcane Initiate and Uncage the Soul. Finally, and possibly most importantly, it is much easier to arrange multiple enemies at a location that contains investigators than an empty one where Dynamite won't hurt your fellow players.

Storm of Spirits is especially good in Sefina Rousseau decks, where it is possible to play Storm of Spirits two, or even three times in a single turn, clearing a location of even tough enemies. And for the truly bold, it can be combined with Double or Nothing though I haven't personally tried this combo yet.

Guard dog is most effective at taking out weak enemies with 1-2 health that deal 1 damage. This allows it to maximize its (guaranteed damage) triggered ability and save a few actions.

Take this example in a Roland deck:

1. Weak enemy (1HP) engages Roland in a location with clues.
2. Roland has guard dog in play, and decides to draw a card (or just walk around like a boss).
3. This triggers an attack of opportunity (AoO), and damage is assigned to guard dog.
4. Guard dog triggers and the enemy is defeated.
5. Roland's ability triggers, and you discover a clue.

Effectively, you've killed an enemy and discovered a clue while using an action doing something else entirely.

Clarifications

-Timing structure (for the above example): trigger action is declared (i.e. move) -> AoO triggers -> damage is assigned (not dealt) to guard dog, triggering its ability -> enemy is defeated -> Roland ability triggers > damage is dealt to guard dog -> trigger action is resolved (move).

-If guard dog has 1HP remaining, it can be assigned both lethal damage and horror (1 damage + 1 horror) from an attack.