The Jellith Dimension is a dungeon.
To access the The Jellith Dimension, players must use a Multijely. Players can use the Multijely on any map which allows use of teleport potions.
Note: The area is not in Astrub. While F2P characters can enter, they won't be able to do anything while there.
The rooms of the The Jellith Dimension are the same as the maps of the The Jelly Peninsula. Each room has 3 random mobs of Jellies. You must kill one of the mobs to progress. For each jelly in the mob, you receive one "jelly pool" quest item of the appropriate color. You lose all your jelly pools after winning the final battle, no matter which color Royal Jelly you fight. If you lose the final battle, your jelly pools will stay in your inventory until you start the dungeon again.
There are 9 rooms of jellies to fight and the 10th one contains the royal jellies.
After completing all the preliminary levels you will come to a screen with all the Royal Jellies, who will have a conversation with each other. You can then speak with one of them, and you will have the chance to fight.
The exact mechanics of which color Royal Jelly you fight are based on the amount of jelly pools you have when you reach the final room.
If you have at least one color with less than 10 pools, you will fight 1 royal jelly. Its color is determined by the color of the royal jelly you speak to. (Not confirmed: You will not be given the option to attack a royal jelly if you have less than 10 of that color)
If you have at least 10 pools of each color, you will fight 2 royal jellies. The colors you fight are believed to be random -- it has not been confirmed that there is any link between the royal jelly you speak to or the color with the greatest number of pools and the mob that you ultimately fight.
If you have at least 20 pools of each color, you will fight all 4 royal jellies. (This is not possible anymore. It used to be the case that Enutrof's Living Chest would also accumulate pools after each battle, and thus Enus would receive double the number of pools as other classes. As of v1.29, Living Chests no longer drop pools and the maximum number of pools you can drop is: 8 jellies x 9 rooms = 72 pools, less than the 80 required to fight all the royals).
There is no definite prize for completing the The Jellith Dimension. However, it is the only place to fight the Royal Blue Jelly, Royal Mint Jelly, Royal Strawberry Jelly, Royal Lemon Jelly and Lemon Jellies which have some useful drops.