Undead monsters are a fact of life in the Seiken Densetsu series. They are dead, but not. It does not have to make sense, it just works.
This Howler is undead.
A few Dragons have been undead.
Ghosts are of course Undead monsters.
The giants of SoM are technically Undead.
Liches are very powerful undead Mages
These Femme Fatales are Vampires.
Vampires are Undead monsters related to Bats.
Zombies are the most common undead monsters in the series.
Skeletons are paired with Green Slimes and show up almost anywhere. They are a reliable source of Keys.
Mummies are found in various dungeons and can only be harmed by the Morning Star, Silver Sword or magic.
The Death Jester
The Death Jester is fought in the Jungle of Illusion. At the beginning of the fight he breaks into three, and only one of him can be hurt. He uses small spells like Holy Ball and Evil Gate, but also has access to very powerful level 3 magics of Air, Water, Fire and Earth. He likes to use Death Roulette which will kill any of your characters in one hit. For some reason he is weak to water.
For some reason someone decided to mummify a big Ape. These monsters are found in various places such as in Lucemia and the Mindas Ruins. As a pet it will increase your attacks against Demi-Humans.
These monsters carry a sword and shield to fight with. They are mainly found in the Bone Fortress and the Duma Desert. Two of the Skeletons encountered in the Bone Fortress are actually the Chobin Hoods killed at the beginning of the game.As a pet they will help you regenerate from a KO faster.
Skull Beasts are a strange undead creature held together by magic. They are very small but have horns, so they do not fit the profile of any living creature. They attack with kicks, rams, and jutting their ribs out at you. As a pet they increase your defense against Undead monsters.
Skeletal Soldiers are the workers of The Death Bringer and hang out in the Bone Fortress. In a Palpota Harbor quest you discover that a Knight has been killed at sea and has become a Skeletal Soldier. When you confront him he attacks with slashes and slides and can blast his arm off at you.
The Iron Centaur guarded the top of the Tower of Leires before Pearl had your character defeat it to get her memory back. Why it was guarding the room is unknown. It carries a Halberd. It’s main attack, Butt Bomb, involves it leaping into the air and then diving down on top of you, while leaping its shadow runs around the room randomly.
Larc the Centaur
After Drakonis had used Larc for what he needed he decided to turn him into a Centaur and sic him on your character in the Underworld. Larc the Centaur has guns in his front legs which he will shoot at you occasionally with his technique Mega Gun. He can also fire off his arms into the air for Fist Rain to have many more of his arms pummel the ground near him. His third attack turns his body splits his body into many pieces and forms an energy triangle that hits you in his Dark Matter attack. After the battle Larc is returned to normal.
Zenoa has the same attacks as Larc. It is possibly part dragon or a bird instead of a horse because it has a beak shaped helmet and tail feathers. It is encountered in the Underworld in the same quest as Larc the Centaur.