Lub Glubs

Lub Glubs are creatures who appear in "Beautopia." They resemble or live inside of inflatable pool toys. The Lub Glubs took over Beautopia, the place where the Hyoomen Tribe used to live.

They emerged from a tunnel with a sign that read "Floaty" posted above it, but the 'O' was dangling down.

They appear as harmless pool toys, in cute varying shapes of ducks, a dolphin, a snake, a pony and an octopus. They are actually vicious shadow beasts that prey on the Hyoomen tribe, as one was seen gnawing meat from a skull that had a bunny-hat resembling Fionna's.

They remained passive until Jake, trying to convince the terrified Susan Strong that they were harmless, tried to pop one with his "pickaxe hand". They spilled and burst from their floaties in hideous pitch-black forms, grappling the heroes with spindly arms. Though stunned by regular attacks, their only weakness seems to be light; aware of this they tried to stop Jake from lighting the massive torch known as the City Heart, and when he did they burned away leaving no trace but the torn floaty toys they were hiding in.

It is assumed that the Lub Glubs encase themselves in pool toys to disguise themselves and protect their bodies from the light, even though it was rather dark in the cavern.

Jake states at multiple times that they remind him of his parents. First a crude outline drawing that reminded him of his father, which made him declare himself crazy, and when confronted by a massive and especially horrifying Lub Glub that he claimed reminded him of his mother.

Trivia

 * Lub Glubs vaguely resemble H.P. Lovecraft's amphibious blob monster the Shoggoth.
 * The teeth of the Lub Glubs resembles that of some Hollows in the Bleach series.
 * The name Lub Glubs is often mistaken as Glub Glubs.
 * It is thought that Fionna exsisted in Finn's dimension but before Finn, proving that the skull might just be Fionna's.
 * There is a rotting cat corpse under the Lub Glub that eating the skull that resembles Fionna.