Character names (if not "Characters" per se) exluding Rick, Jennifer, and Biggy Man:
Water_Hand -- bluish hand, top-left corner, known in US as "Monstrous Hand". This creature is the hand of a "Water_Dead" coming out of puddle.
Poltergeist_(Splatterhouse) -- picture frame with single eye, Stage II boss.
Evil_Cross -- inverted cross, top-middle, Stage IV boss.
Hell_Chaos -- giant hand, top middle, Stage VII boss.
Fire_Dead -- humanoid on fire, top right. This creature is a "Dead_Man" on fire.
Mirror_Rick -- Rick's reflection in mirror top-right.
Hanging_Dead -- thing resembling a "teruterubouzu", top-right. This creature is actually a zombie hanging from a noose.
Evil_Dog -- top-left under "Water_Hand" and "Poltergeist_(Splatterhouse)", known in US as "Zombie Dog". To the best of my knowledge, ordinary dogs turned undead due to feeding on undead flesh of zombies and "Dead_Men".
Top_Heavy -- next to "Evil_Dog". This creature is a top-heavy (hence the name) "Dead_Man" due to having an enlarged brain, which allows its head to fly when its body is destroyed.
Master_Dead -- skeleton in cloak and witch's hat in middle, not to be confused with "Dead Master" of "Black Rock Shooter". Undead necromancer, responsible for the NORMAL zombies inhabiting the Splatterhouse.
Woody_(Splatterhouse) -- disembodied hands in front of "Master_Dead". This creature is an zombie hand, inspired by "Evil Hand" from "Evil Dead II".
Picture_Ghost -- head coming out of picture frame. Undead spirit INHABITING (not manipulating) picture.
Water_Dead -- bluish humanoid with "Evil_Dog" on its head. This creature is a water-dwelling "Dead_Man" that slightly resemblances DC's "Swamp Thing" in the game.
Ova_(Splatterhouse) -- the three smaller creatures. These creatures are newborn "Dead_Men", freshly hatched from floating eggs (hence the name?).
Knoboo -- pink thing near centre, known in the US as "Slug". This is the OFFICIAL Japanese romaji for this thing, katakana ノブー Nobū.
Joker_(Splatterhouse) -- blue ghost girl, likes to slam-dunk skulls onto Rick's head.
Crow_(Splatterhouse) -- similar to the "Evil_Dog", ordinary crow turned undead from feeding on undead flesh.
Body_Eater -- red snakelike thing, known in the US as "Boreworm". Leech-like creature feeding exclusively on the undead, sometimes from the inside out.
Dead_Man -- purplish-grey creature with "Body_Eater" on its head, known in the US as "Red Walking Zombie". Not a zombie (living turned undead), but a new species of living-BORN-undead humanoids hatching from eggs SPAWNED from a "womb" in basement, undead gore having grown mold-like throughout the Splatterhouse.
Green_Dead_Man -- greenish-grey creature next to Ric, known in the US as "Green Walking Zombie". Leveled-up "Dead_Man", requiring two hits to kill.
Revival_Dead -- skeleton, raised ("revived") by "Master_Dead".
The remaining creature seen "drooling" on the "Revival_Dead" skeleton is most likely one the zombies seen chained to the wall that projectile-vomits when Rick comes near it. Like the "Hanging_Dead", whether or not these creatures were zombified BEFORE or AFTER what Dr. West did to them is unknown. My best guess is that West employed the "Master_Dead" to create zombies via magic so that he could reverse-engineer the process via science.