Golem

This character originates in Jewish Mysticism, and was the basis of a book by Gustav Meyrink, Der Golem, published in 1925 or so and appeared in a film by the same name starring and produce by Paul Wegener. In the story, a Rabbi brought the Creature to life only when there was a clear need, to defend the Prague Jewish community from expulsion. A version of this character has appeared in both Marvel and DC comics.

Marvel

In this version: In centuries agone, they called the Golem a Myth, a creature formed of stone and clay and from the blood of a peoples' oppression,- a moving monolith who rose before the yoke of tyranny-shattered in his monumental fists- then vanished into the sands of time-there to be almost forgotten-until today!
Now, once more, the Golem rises-summoned from his eons-long sleep to protect those he loves. Now, for the fist time in untold decades.......THE GOLEM WALKS! Golems have also come up against Moon Knight and the Hulk.

In a tale scripted by Len Wein (co-creator of DC's Swamp-Thing) one Professor Adamson found what others said was just a statue, but he believed it to be the Golem. With his dying breath he read from ancient scrolls he possessed in a frantic attempt to revive the Golem to help his friends, and when his tears fell on the Golem's foot this brought it to life. (Strange Tales #174)

DC

At the competition a golem has shown up in some Batman comics, Swamp-Thing, and also in Ragman. In that appearance the Golem went on a rampage and Ragman must destroy it.

Other publishers

The figure of a Golem features in James Sturm's story The Golem's Mighty Swing, published by Drawn and Quarterly in which a member of a depression era Jewish baseball team is talked into dressing up a Golem as a publicity gimmick to tie-in with the film's popularity.

IT!

Based on the 1940 story by Theodore Sturgeon, an adaptation of which appeared in Marvel comics' Supernatural Thrillers # 1, (1972). It tells the story of a plant creature formed around the skeleton of a man. It wanders around the swamp interacting with members of a local family.

The Heap

Originally published in Airboy Comics (Dec 1942), he was a WW1 German pilot shot down whose will to live, coupled with the vegetation of the swamp and some mystical force allowed something to rise from the swamp. Image have a new version of Heap as well.

Solomon Grundy

The character made his first appearance in All American #61 (October 1944). In Starman #34 (Sept 1997) we are told that one Cyrus Gold, a wealthy merchant, was murdered by rogues in the swamps of Gotham City during 1894. Some anger at his death or rage at the world kept his essence in the swamp. 50 years later that essence took form and was reborn. He encountered some hobo's who named him Solomon Grundy because he was born on a Monday.

Alan, the Killing Tree!

In the story 'Invitation to Doom' from Witches Tales #7 (Harvey, January 1952) Alan the botanist thinks that trees hold the secret to longevity so he replaces his blood with some sap, unfortunately this has the unforseen side effect of turning him into a homicidal tree, and the local authorities have no choice but to put a stop to his murdering rampage.
Information care of Matt and Klaus @ UltraZine
According to the Eerie Publications Index the plot was later reworked for the story 'A Shape of Evil' in Terror Tales Vol 5 #1, Feb 1973.

Glob

The Muck Monster

Swamp Thing

The Stalking Swamp

Ironically enough, though, this WAS the same swamp in which the real Swamp Thing would later dwell. Rick believes he met Zachary Nail in issue 12 or 13 of his own original run. (Len Wein, who co-created Swamp Thing, wrote both that story and the Dr. Thirteen one, though original artist/co-creator Berni Wrightson had already been replaced by Nestor Redondo at that point.)

Big thanks to Rick.

Turd

Mudd

Written by Man-thing co-creator Roy Thomas and art work by Scott Shaw This character made a one off appearance in Captain Carrot and his Amazing Zoo Crew NO 4 (June 1982). A carelessly discarded drum of make-up goop combines with an alligator's skeleton and creates MUDD.

Elf-Thing

Eclipse Comics, Mar. 1987. Story, Frank P. Marino ; art, James J. Friel.
The Comics Warehouse says A quadruple parody of Marvel's Hulk, Hillman's (and Eclipse's) Heap, DC's Swamp Thing, and WaRP's' Elfquest, in which a muck monster research scientist ingests a secret serum that turns him into (gasp!) a hideously cute elf. How could they not mention Man-Thing???

Sludge

Bog, Swamp Demon

Real name: BAUGGROTH
Occupation: Demon of the Lower Pits. Height: 82, WeIght: 255 lbs, Eyes: Black. Known super powers: Demon strength. Burgeoning, magical abilities attributed to spellbound bones that Bog has borrowed to build his body.
First appearance: Teenage Mutant Ninja Turtles #4 Vol. 2
History: Bog was freed from the boiling depths by escaping through the Hell Well. A twisting, turning tunnel magically excavated by a long dead wizard. It seems the necromancer wished to possess the secrets of Hell by breaching her walls, but he only perished in the process, succumbing to a fiery demise at the very foot of this 'Hole Down to Hell. Now, centuries since, Bog arrives to step foot upon this plane of existence, only to find his ectopiasmic essence must have form. Thus, finding the barren bones of the long dead sorcerer, he adopts them as his own and weaves a body from the muck and undergrowth of the stagnant, sloppy swamp. Bog has yet to fully realize the magical powers trapped in his borrowed skeleton, although they are beginning to manifest themselves as he does battle with his many foes who would once again seek to drag his soul to Hell. Bog has fought against such evil fiends as Mogog the Prince of Darkness, Baphomet Etherlal and the Hideous Hellaphant, Beast from Beyond. Needless to say, Bog has triumphed over them all. He and his swamp land home are safe for the moment!
Publishing history: TMNT 04-12 Vol. #2, Bog Swamp Demon #1-4, Guest Appearance in Hall of Horrors #1, Big Bang Comics #15. Bog Swamp Demon Blogspot

Pinus Radiation

The New Zealand entry in the Muck Monster legion by Peter Johnstone. A tree's roots tap into an ancient meteor, bringing the tree to life. As it goes on a rampage, a jet pilot crashes his plane in the forest. Near death, he agrees to merge with the tree, thus giving rational control to the tree's brute power. Copies of the comic are available from here.

A visitor remarked that Pinus Radiation seems to have a lot in common with two characters created by Steve Streeter - Xyloman and Root, which we now have some information about below...

Groot

November 1960 issue of Tales to Astonish. Claiming to be monarch of his people, Groot came to Earth to steal a village and return it to his home planet for his scientists to study and experiment on the inhabitants. First discovered by biologist Leslie Evans, Groot attacked the town and was eventually killed when Evans released specially-bred termites upon him. - Not a muck Monster

Keith Giffen made a brief use of Groot in his 2005 Nick Fury's Howling Commandos limited series, then gave him a staring role in Annihilation Conquest: Starlord as part of a team on a suicide mission. This lead to a role in the ongoing Guardians of the Galaxy title.

Thanks to Greg Plantamura for nudging me to update this entry

Xyloman

An alien probe fell to earth, and dying, transferred it's energy/life force into a tree. Chuck Powers, forest ranger sleeping out in the woods, went to investigate. The energy / life force decided it had a better deal with Chuck, and entered him next. He gained tree related powers (regeneration of lost limbs, and stretching fingers - how he retracted them based on plant growth wasn't well explained) and extraterrestrial powers, such as the ability to fly. He absorbs tree and alien powers... but he doesn't change from into a heap or anything, he appears the same as he always did, except when his fingers do that growing thing.. Created by Steve Streeter

In a collaboration with writer Klaus Haisch, Xyloman meet a tree based foe by the name of Root, a normal tree turned ambulatory by the wicked Abby Cadaver, Root wound up pulling Abby Cadaver down into the fires of Hell. Klaus pointed out that Root owes alot to Groot. Thanks to both Matt Love - who inked the last few issues in 1977 - and Klaus Haisch for supplying the information and scans.

The Bog Beast

A character in Larry Lieber's Atlas Comics line in the mid-seventies. He appeared in Tales of Evil #2, Weird Tales of the Macabre #2. He doesn't appear to have any powers other than metahuman durability, and is apparently part angel and part demon. In the Tales of Evil #2 story ( The Fifty Dollar Body!, 8pp) he encounters hippie revolutionaries, and sides with them and against the police who try to kill them. The female tries to sell him to a circus, the male gets him out. The woman shoots the man and flees, tripping and falling, hitting her head on a rock, dying.

The credits for this story are John Albano, writer; Jack Sparling, artist; Alan Kupperberg, letterer; Larry Lieber (Stan Lee's brother), editor. Cover art ??
Information care of Scott Andrew Hutchins

The Swamp Creature

A jigsaw puzzle over 200 big,scary pieces made in 1974 by American Publishing Corp., Watertown, Mass, 02172, USA. (ref.#1186)

I've also seen mention of a swamp creature in UNEXPECTED #152, any details?

Un-named Creature

This creature appeared in the Dungeons and Dragons animated TV series episode Prison Without Walls in which the party of adventurers have to free a village of enslaved gnomes from the villainous Venger, who is using them to mine mystical gemstones for him. Along the way they encounter the creature.

While we don't know enough about the creature to be sure it would count as a Muck Monster, as the episode was written by Steve Gerber I think it deserves a mention. You can find some more details at Branded in the '80s