Set Size4
Number of unique Cards2
RoleDoom, Enemy, Discard
Threat LevelHigh
# of scenarios2
Appears in: Lost Sister, Thing from the Depths

This set is used only twice during the campaign. Actually, since those two scenarios are among the five optional ones, you can get through a whole campaign of Hemlock Vale without ever encountering Mutations. When you do shuffle these cards into the encounter deck, it is worth taking note of that, however. Because while it’s only four cards small, it does pack one hell of a punch, both cards in it are very powerful and you will usually not appreciate seeing these in your mythos phase.

Threat Level: High.

The treachery has two largely unrelated modes, depending on if there are enemies around or not. And both sides are rather nasty. One of the very few cards in Hemlock Vale that deal with doom which is of course always something to take note of. However, placing a doom on an enemy does give you a good way out. So when this doom lands on an enemy that you were going to kill anyways, you can gain some momentum here by clearing two encounter cards in one go. Notably, this isn’t restricted to non-Elite however, so this doom can end up being placed on The Thing from the Depths or the Chelydran Hybrid, which all but removes the option to defeat the enemy to take care of the doom. Often, this will affect an enemy that you decided on leaving behind, for example a Black Amanita, making you regret or at least rethink that decision as you will likely want to backtrack and kill it after all.
So while there are some cases where the added doom is taken care of swiftly and without losing any more time to it because it ends up on an enemy you wanted to kill anyways, there are absolutely enough bad cases around to make this a scary card.
Should there be no enemy on the board at all, which basically only happens during Lost Sister (and it’s not particularly likely there either), then the random discard of two cards hits hard as well. Possibly even harder than the doom.
Now, with all that unpleasantness out of the way, there is one silver lining here: The doom placed by Unnatural Growth does not force the agenda to advance. So if you draw this card during the “Witching Hour”(the turn before the agenda advances anyways), you get a freebie.

Threat Level: High

Sudden Mutation plays into something that Hemlock Vale pulls off fairly often: Making you have to deal with multiple enemies in one turn. When this finds its way onto an enemy you need to kill, you will not be able to properly plan your turn ahead because the variety of enemies waiting for you in the encounter deck is pretty massive. While Sudden Mutation will only attach to non-Elites (so not to the Thing from the Depths, Shelly the Hybrid or any of the big crabs in Lost Sister), it has no restrictions on what it can reveal from the encounter deck through its Forced effect. The limitation to the Mutated trait doesn’t apply then either, but that trait is cosmetic anyways – all the enemies in the respective encounter decks are Mutated.
A common thing that happens with this during the Thing from the Depths scenario is that it attaches to one of the tentacles of the Thing. Which you will then have to deal with to protect Shelly. And which will then either roll into another tentacle… or something even worse like a Cochleal Stag. Note that the enemy isn’t necessarily spawned engaged with you, meaning that if you have multiple fight-ready investigators at the location, the second enemy can be engaged by a different investigator, preferably one that didn’t take their turn yet of course. It does however also mean that Aloof enemies (Amanita, Forest Watcher) will get to do their aloof thing.
This is a very dangerous card and like Unnatural Growth it does come with a hefty amount of bad cases that will put a lot of pressure on you. You will sometimes see Sudden Mutation attach to an enemy that you might be okay with not defeating. Like a Black Amanita or a Poisonblossom. This can allow you to ignore Sudden Mutation… but you do risk that this enemy experiences some Unnatural Growth or a Call of the Wild later on, so weighing the risks is important there.

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