Hello I'm sure you have seen the Slooms on the wiki if not so look at them here http://wiki.spiralknights.com/Lichen
Slooms are creatures that inflict sleep so i think they should be brought back as they have trinkets and armors that resist sleep right? so then there will be at least one thing these would be useful for.

The Castle of Sleep would be similar to The royal jelly but instead of pink it would be blue and you can get sleep effect.

as you know slooms have a larger variant called sloombargos which are pretty damn hard these would show up at most of the levels.

the layout would be virtually the same as the royal jelly but when you are on the second level with the keys past a group of monsters, the one to the upper left would be with 3 sloombargos and more slooms along with some explosive jellies. The last part of that level similar but instead of lichens and tier 2 jelly cubes there would be slooms and sloombargos.

then on the last level would be a cave with blue crystals as you go along then you would see a gate with four heart generators in front of it.
You would enter to see The Sloom Lord who would be like a cross between Royal jelly and Sloombargo he would look like a Sloombargo with spikes and his core would be a shining silver.

like the jelly king you attack till his core outer shell shatters revealing it to be a dark pulsating purple when this happens he spawns four sloom polyps (like ordinary polyps but blue and with a spike on top and they inflict sleep) they would spawn one sloom as an attack and only one can be spawned per polyp and then they would fire spikes at you.

after killing the turrets the whole Sloom Lord turns purple and he spins around rapidly firing spikes and doing damage if you touch him.he then PUTS TIME TO SLEEP for a short period slowing everything dwon and making him slightly faster. You move only slightly slower but when you shoot your bullets travel slowly.

when he stops you attack more till he explodes which starts to cave in the cave so you have to escape.

the levels would be called in the following order
The Tired Hall

Sleep's sanctum

Time's Cradle

The music would be the boss music but slow and played on harpsichord.
when you reach the Sloom lord the music speeds up and you hear a slowed down triangle every 3 seconds in the music.