Hybrid Animals

 are creatures that Doctor Gross had created using two distinctly different species on animals and monsters. In some cases, such as Diamond Komodo Dragon, it is one species of organism combined with a mineral. In all cases, the Hybrid Animals possess bionic upgrades, and this allows Doctor Gross to control them. They make another appearance in "Reboot," but only the unnamed Eel-Dragon, referred to as a 'giant electro-eel' by Finn, makes an appearance in the episode.

Diamond Komodo Dragon
The Diamond Komodo Dragon is the first hybrid to be walked passed. It isn't given much attention by the characters, nor do the camera angles pander to it. Once transformed it's eyes turn static identically to the other hybrids, and becomes bipedal with thick appendages both upper and lower.

Fly Flan
Fly Flan, given in the its name, is a combination of a fly and a Mexican dessert. They have a tendency to be seen with prominent rear-ends, a common gag in Adventure Time. Fly Flan isn't seen to transform in "Preboot," but is found outside after everyone escapes the vessel.

Shark-mouse
Shark-mouse is said to be "a shark that breathes air," despite the juxtaposition is still seen living inside an aquarium, although this could be so that it can move around without transforming limbs. It could also be amphibious to an extent, being able to breathe through gills or lungs depending on the situation. It's entire body is made of the shark, while its face is from the mouse. When transformed it contains powerful upper body appendges, but disproportional legs.

Chicken-bee
Chicken-bee has most of its body influenced by a chicken, with bee-like features added to it. Despite being referred to as a Chicken-bee from the concept art, Doctor Gross claims this hybrid has wasp wings. When transformed into its submissive state, the borders between the yellow and black striped pattern sprouts buzz-saws. Jake seems to admire Chicken-bee, as he pretended to snap a picture of it.

Scorp-munk
Tiffany provides the name for this hybrid, and this is the only hybrid that appears to possess sapience. Similarly to chipmunks seen in other episodes such as "Bun Bun," he possesses the ability to speak English, albeit with a relatively deeper voice. He attempts to warn Finn and Jake through a dance, but is unsuccessful in transferring his intended message. Scorp-munks transform with robotic claws that extent from under their feet, and extremely sharp teeth.

Wolf-lards
Wolf-lards were called upon by Doctor Gross, who are here assistants, when she was going to insert an implant on the trio. They are said to get both their high endurance and killer instincts from the Sea Lard portion of their mash-up according to Tiffany, although this could just be verbal irony. When under Doctor Gross's control, they do not appear to undergo any noticeable morphological change; only their eyes change.

Gator-squid
The Gator-squid is briefly seen, and is not given a lot of screen time. It may possess the same amphibious abilities that the Shark-mouse does. When transformed, the ends of its appendages grow three bionic fingers each, presumably to aid its movement across land. Along with this, its jaw is extended by a hydraulic.

Spider-turtle
Spider-turtle is given no special attention is its debut. It can be seen when Doctor Gross leads Finn, Jake, and Susan into her menagerie, and when seen appears to leave its head exposed, with all appendages inside its shell. This hybrid is not seen anywhere outside after the vessel explodes.

Electric Eel-Dragon
A very notable hybrid, and is seen in both "Preboot" and "Reboot." This hybrid goes without an official name, neither being named within the episode, or having its name given through the concept art. However, this hybrid is referred to as a "giant electric eel," by Doctor Gross, and "a giant electro-eel" by Finn. It is a gargantuan creature, and along with its ability to fly and send electric currents makes it very formidable. This hybrid does not undergo any visible transformation.

Time Bear
This hybrid is referred to as "a guy that knows what time it is," who is also one of Gross's best. He makes his first appearance in the episode "Hoots," although this was actually inside a dream Finn was experiencing. What his name is or what his species is called is not given. When he transforms, he increases in size taking on the appearance of what a typical grizzly bear looks like.

Apple Hybrid
Not much is seen from this hybrid in comparison to the other Hybrid Animals seen in "Preboot." This hybrid is shaped as an apple, with its other counter-part unspecified. It is not seen to transform, nor is it seen outside the vessel when the others escape. This hybrid's identity goes unknown.

Trivia

 * The Fly Flan isn't seen to transform nor chase after Susan, yet somehow makes it outside.
 * It is unknown how the Electric-eel Dragon escaped the vessel, as there is no exit large enough for him to get out of.