This article was first broadcast in Episode Two Hundred and Thirty Four on 8th February, 2023.
Note: This article was adapted from an episode script, and so there may be parts that don’t flow well when read, because they were initially designed for broadcast.
Thessalar is a minor figure in the grand scheme of things, but his popularity got a slight boost a few years ago, albeit indirectly.
A huge, amorphous monster appeared toward the end of Stranger Things season 1 and in the trailers for Stranger Things season 2. Given how much Stranger Things leaned on D&D for story elements and naming conventions, fans of the series and D&D immediately began to guess what the monster was or would be called. With no clues from the cast or writers, the internet as a whole eventually went with “thessalhydra.” And then a lot of people only familiar with 4th and 5th edition D&D went, “a what”?
By the way, the creature from stranger things was eventually dubbed a mind flayer, but that’s not important right now.
The thessalhyrda is a monster out of 1st edition. It originally appeared in the second monster manual. Like many monsters of that time it did not have an extensive lore history to go along with its existence; it was just another horrifying creature you could run into in swamps, jungles, and caverns and turn your caving expedition into a nightmare. It was reprinted for official resources in both 2nd edition and 3.5. It took 5th edition longer to get around to it, and it’s still sort of hidden away in a secondary adventure.
The thessalhydra is a lizard-like creature with a reptilian body that is 36 feet long, 20 feet of which is tail. At the end of the tail are sharp pincers. It has four legs and the top of the body is a mess. Where most creatures would have a head, it just has a humongous round mouth. Around the edges of the mouth are eight snake heads. All of the heads spit acid, and the creature is large enough to swallow most other regular sized creatures if they get anywhere near the main mouth, which is also dripping acid.
When the creature eventually got some lore, it was mostly to just describe it as a horrifying but dumb beast that terrorized and/or ate anything that came near it.
However, the lore eventually added the fact that thessalhydras are unusually good breeders.
This led to the creation of an entire line of what are called thessalmonsters. You have the thessalmera, which is what happens when a chimera meets a thessalhydra in breeding season. It looks just like a thessalhydra, except instead of the large mouth in the middle of all the snakes, the lion head is there. And then behind the snake heads on its back is the red dragon head that breathes fire.
Next you have thessalgorgon. Remember in D&D a gorgon is a large bull-like creature covered in metallic scales; all the nice ladies with the snake hair and stony gazes are called medusas. So cross the bullfighter’s worst day with a Thessalhydra and you get a thessalgorgon, featuring metallic scales and a bull’s head that breathes petrifying gas.
You would think you could guess the pattern but then the thessaltrice has to go and subvert expectations. This beastie, again, favors its thessalhydra parent but it keeps the gigantic round mouth. Instead, the snakes coming out from around the mouth don’t have snake heads, they have little cockatrice heads, each one of which can petrify whomever they bite. It was also rumored the thessalhydra bred with other creatures and got them pregnant, but none of those creatures lived once born.
In the lore, it seemed, all of these horrific creations were assumed to be the result of thessalhydras being unusually prolific and the various nature gods of the planes all simultaneously going “yeah, I’m not dealing with that. It happened, just ignore it until something kills it.”
It wasn’t until much later, specifically Dungeon magazine 134 for edition 3.5 that another source for these things was suggested.
Thessalar hails from Greyhawk, where he spent much of his time obsessed with the idea of understanding life and creation. But unlike rangers or druids who try to live in harmony and learn from nature, Thessalar wanted to replicate the ability to create new pieces of it. He became incredibly adept at grafting and mutating living creatures with magic and alchemy. The thessalhydras are supposedly his creation, and are one of the few that survived. All of the various dead half-breed creatures people found or reported were not a result of biology giving up after birth, but instead of failed experiments by Thessalar.
Thessalar is mostly a self-absorbed narcissist and as such ignores any hypocrisy or contradictions in his own work. For example, when he hadn’t finished his work on trying to create life as the end of his own approached, he went through the effort to become a lich. He then proceeded to use the power of several wish spells to begin formulating a “proto-life solution”, rather than simply using the spell to create whatever he had in mind.
Reinforcing the narcissism thing, the adventure from the Dungeon magazine says he became obsessed with a female celestial hiding out near the area where he’d made his lair. He was unable to fathom why she wasn’t immediately smitten with him and rebuffed his advances. To solve that problem, he tried to craft a domination potion to bend her to his will.
In addition to the thessalhydras and the various related subspecies, he also claims credit for creation of almost all monstrosities in the world. Owlbears, chuuls, rust monsters, and mimics are supposedly his doing. Chuuls and mimics have been mostly proven to not be because of him specifically, but a lot of people concede the owlbears and rust monsters could very well be things he cooked up. Also, nobody disputes his claim about the various thessalmonsters because he’s shown an ability to immediately and effortlessly command all of them whenever they’re near him.
Fifth edition has only used Thessalar once and like many things his basis and existence has changed a bit. He appeared in the Extra Life resource “The Infernal Machine Rebuild” where he is a self-obsessed artificer, albeit one that is searching for ways to prolong his life and may be in the early stages of searching for lichdom. In addition to the thessalhydra, he has also created a thessalkraken.
In general, however, both Thessalar and his creatures are somewhat nerfed from previous. As a mortal spellcaster Thessalar is a lot less of a threat. He still weighs in at CR 14, but lacking undeath he is a lot easier to vanquish, and he doesn’t have the innate control over all thessalmonsters that he did in other editions. Also, the 5e Thessalhydras are only CR 4, which is a huge threat reduction from previous editions where parties were expected to have levels in the high teens before fighting thessalhydras was something they should even think about.
If you want to pick up the Infernal Machine rebuild, that’s probably the easiest way to make use of Thessalar and his lore in 5e. He could also be lifted out of that resource and used as a Frankenstein-like figure in any number of places or situations, either as an incidental threat to an area, a lackey of a bigger bad who’s making use of him to manufacture monstrosities, or just as a threat in his own right that needs to be overcome.
If you want to go with the lich incarnation of him, even in his previous versions he didn’t differ much from a traditional lich except in his ability to control the thessalmonsters. That is easy enough to just implement as a DM without modifying or making up any rules; the thessalmonsters just become companions for the lich.
Scaling the thessalhydras back up to their former glory, or using any of the other thessalmonsters that didn’t get 5e stats, probably requires some more work. But you can also comb through official or third party resources for non sapient creatures with the “monstrosity” type. Reflavoring them as thessalmonsters only requires a little bit of work with naming. Or you can just keep them as-is and claim Thessalar is making them. Things like froghemoths and dracohydras are certainly on brand for him.
So if you need a monstrosity generator, or just another lich with a well-known name that isn’t Acererack, Thessalar is certainly an option.