Jelliens are evil alien versions of jellyfish that were created by the Jellien Leader after it consumed and trapped a regular jellyfish. They appear in the episode "Planet of the Jellyfish." They are minions of the Jellien Leader, and go and bring bodies of fish to it.
Jelliens look like regular jellyfish, except they have big, shiny, pitch-black eyes. They have mouths with sharp teeth in which they use to consume people and make Jellien clones. When creating said Jellien clones, they generate tendril-like tubes that are used to secrete colored biomass that quickly forms into the said clones.
Being a mere clone of jellyfish, they cannot sting.
Abilities, talents, and relationships
As servants for the Jellien Overlord, Jelliens explore and take the role of drones. This is because they capture non-Jellien life forms and create the Jellien version of the said lifeform while taking the original to the Jellien Overlord. They also scout over non-Jellien lifeform territories and stumble upon Bikini Bottom which provided them more prey.
While they appear to be weak noticeably as they cannot sting, they counteract this via manipulation and trickery, as shown where it uses its appearance to fool SpongeBob. However, if necessary, they also willing to fight to the death with their enemies.
Primary Jelliens have the alarming ability to copy the captured victim's DNA that are both used to create the Jellien clones. As a result, while its appearance mirrors the original, except for the eyes, which remain the same with other Jelliens, Jellien clones would easily blend with non-Jellien life forms while either hunting for more potential victims or guarding the Hive/Overlord's lair.
Role in episode
During the beginning of the episode, after SpongeBob passes by a cave, the Evil Alien Jellyfish Overlord eats a jellyfish and makes them into Jelliens. One of the Jelliens eats Patrick and makes a clone of him, and Jellien Patrick is born. The rest of the Jelliens are then captured by Jellien Patrick and they both give out the Jelliens to the citizens of Bikini Bottom.
Afterwards, the Jelliens manage to take over most of the citizens except SpongeBob and Sandy, who both learn that the Jelliens' weakness is mayonnaise. They then fight through the Jellien army using mayo and eventually take down the Overlord. The Jelliens are all destroyed, reduced to relish and are never to be seen again.
The name "Jellien" is a portmanteau of the words "jellyfish" and "alien."