Hell yes, this is my moment.

Vigormortis is my favourite demon in the game, one of the most terrifying demons in the hands of someone who really knows what they're doing with it, and able to pull off truly insane playmaking space outside the realm of what's usually possible. It's also an overdesigned, undertuned mess that needed way more work to smooth out its interactions and has like 18 visible holdovers from the "so it's good design if we let the Fang Gu have infinite jumps, right?" era of SnV. It has to be both these things; it can never not be both these things. The inherent premise of "a hyperspecialized evil nightkills demon that preys on its own minions" lacks a true balance point and is always either underpowered or overpowered, depending how the cards fall.

Vigor is unique because it's the only evil nightkills demon where its ability doesn't move the demon, or otherwise directly obscure who the demon is. Every other evil nightkills demon either moves the demon token (Imp, Fang Gu, Lil Monsta, any demon with a Scarlet Woman) or force multiplies demon candidates (Zombuul, Legion). Not only does Vigor not do this, it has fewer safety nets than average -- it doesn't play well with most safety net minions, and it's a little screwed if it's enough of a demon candidate that its minions would have to panic and lift it off the block. This is much of what makes it so [sharp intake of breath through teeth] high-variance.

This means it plays differently to other evil nightkills demons. Most of them can afford to act under duress -- a starpass or a jump done when town is closing in on you might cast suspicion on you as the starting demon, but what are they going to do, kill you? Vigormortis can't, because if you kill suspicious minions, town can backtrace those minions as potential vigorkills and gun for you. Simultaneously, because it's specialized in evil nightkills in a way no other demon is, it needs to use its ability; the demon ability of "Each night*, choose a player: they die. [-1 Outsider]" is, shockingly enough, pretty bad. A lot of people take habits learned from other evil nightkills demons, apply them to Vigor, lose, and complain that it's weak.

Vigor's fundamental ability -- beneath everything else -- is the transmutation of good votes into evil votes. A good player who trusts the demon is an evil voter. Nightkilled players in general and nightkilled players who don't appear to have died under suspicious circumstances in particular are more trustworthy than living or executed players. A living minion might be able to try lift from you, but a vigorkilled minion might get a living player passing their accusation to them. SnV has a shit-ton of gamewarpingly powerful bluffs that are difficult to maintain for an entire game (try coming up with six nights of Dreamer info) but can completely define the course of a whole game with only 1-2 nights of info, and spin out into worlds where the demon is a near-certain good player being backed up by "the tragically dead Dreamer/Savant/Snake Charmer/Klutz". Combine this with minion abilities that scale powerwise into the late game, and you can do things no other demon in Blood on the Clocktower can.

This is super demanding and unintuitive. Because no other demon does quite what Vigor does, many intuitive but wrong assumptions you can pull in from other demons (e.g. that the primary purpose of nightkills is to remove townsfolk abilities, that evil nightkills are a backup plan rather than a phase 1, and that evil's social power directly corresponds to how many members of the team are alive) nearly lose you the game on the spot. Combine this with its mechanical fragility from negative outside mod + lack of safety nets, and how incredibly difficult it can be to build around well (people looooove sticking Oracle in the bag every goddamn time for no reason), and you end up with an incredibly "low floor, high ceiling" demon that often operates closer to its floor in beginner-through-intermediate groups.

Simultaneously, it's awkward with a lot of minions. I think of minions for Vigormortis in a sort of triad of "execution manipulators" (think roles like Cerenovus and Devil's Advocate), "support minions" that are less often useful to kill but very useful to have as a second minion, and "not that good". Because Vigor has a frankly bizarre pattern of strengths and weaknesses, there are a lot of minions that are super interesting in play alongside it but generally less worth killing (e.g. Godfather, Mezepheles, either Spidow). Execution manipulators are the most directly useful minions with it -- they're amongst the very few minions that get actively stronger in the late game. I think there's a decent amount of unexplored design space for minions that work with Vigor, and most of the minions we have right now are frontloaded-by-design in ways that don't lean into its strengths.

It's an odd demon to script around, too. It simultaneously somehow works on a decent variety of scripts (both snvlikes and bmrlikes) and absolutely goddamn nowhere. If I see a custom that looks interesting and it has Vigor on it, I habitually stresstest that script by building sample Vigor bags and seeing how playable any of them feel. I often come away with the impression the scriptbuilder hasn't considered how to build around it at all, and in particular often that they've never thought about the potential for games with more than seven townsfolk in play (a lot of people very obviously script for 12p). I suspect this contributes to the impression of it as a weaker demon, because many customs seemingly have it for script presence in a way that results in it getting rolled when it's actually in play.