(EDIT: Updated for feedback and new FAQ.)
This is an older enemy, and a lot of this review may come off as obvious to more experienced players or has already been mentioned in reviews for other relevant cards, but I figured for the sake of those less experienced (or if nothing else just for fun) I'd write an extensive breakdown of this absolute monster.
First, the elephant in the room (the towering, invisible elephant): They can only be damaged or attacked with Esoteric Formula. The highest impact of this interaction is that your usual sources of extra damage are gonna get benched. I'll go into more detail on that, including a few workarounds, later on.
It has 6 Fight. That's a problem, but it's fair; your chance of landing a hit unaided against an invisible monster would probably be very low. Have your nimblest investigator pack the magic dust and grab some clues for those location effects. Mystics are at an advantage with their high , but with enough clues on your target, everyone should be able to hit consistently.
It has 3 Evade. That's a fairly lax difficulty for high investigators. Since it's Massive, and attacks for 2/2, you'll want someone to Evade basically every turn, if you can't secure the kill. Rita Young with Track Shoes and Peter Sylvestre is a star, she'll be able to dart around the map and keep threats down with aplomb.
Its health is 1 + 1. What this means is that in a 3-4 player game, at 1 damage per action, you won't be able to defeat it in a single turn. How do we get around that? If you're trying to get extra damage, you're gonna be ice skating uphill. (EDIT: No "additional damage"/"move damage" effects work.) Esoteric Formula uses , meaning Vicious Blow (and The Home Front) is out. Double or Nothing technically works, but is extremely inefficient—it brings the difficulty to an insurmountable 12, so you'll need a whole lot of clues or effects that can reduce the difficulty, all for one extra point of damage. Barring that, Zoey Samaras (via her ) and Lita Chantler seem to be the only ones capable of cheating out extra damage. Lita has amazing value here, but good luck getting her this far, un-sacrificed (to not one but two Ancient Ones!), with at least 3 mental trauma under your belt, and drawing her in time to make an impact.
For everyone who isn't a crazed zealot, leveraging extra actions is the way to go. Rogues should have no problem with that. MVPs here are Marie Lambeau, who can use Esoteric Formula with her free action; Stella Clark with Oops! and the usual gaggle of nonsense; and Tony Morgan, who in addition to being a Rogue can place bounties to get his free Fight action (but only on Brood that enter play after the game begins) (EDIT: He can use Bounty Contracts during scenario setup, thanks Nenananas!).
So that's some pretty sound strategy, but you're not interested in that. You came here for the jank, the cheese, the cherry-tapping, the Air Bud clause! Years ago, Django astutely pointed out the absence of the Elite trait, but at the time the options this opened up were less than stellar. Time went on, and more cards came out; these are mentioned in the comments of that older review, and have quite a few reviews of their own mentioning their use against this enemy. The two that take the cake here are Waylay and "I'll see you in hell!", because while the text on this enemy prevents it from being attacked or damaged by non-prescribed means, you can still defeat it any way you like.
Evade into Waylay + Resourceful is an easy combo for high Survivors (did I mention how good Rita Young is here?) that comes at a paltry two actions and a mildly spicy 3 resources. Mix in your favorite methods of guaranteeing success, keep the resources flowing as much as you can (On Your Own will help here, especially if your football friend ended up on the altar last scenario...), and if you’re feeling extra cheesy, recur it infinitely with True Survivor.
"I'll see you in hell!" is so-so by comparison given the cost, but with a favorable board state, it's a tactical nuke. Using it on as little as two Brood could still be considered a good value trade in certain circumstances. This is a questionable include for most Guardians, but Calvin won't hesitate.
If all else fails, swallow your pride and Resign. The better you did last scenario, the harder this one will be, and defeating all five is a tall order.
