So my suggestion is a Nova class monster.
These monsters appear as a energy, A small core, surrounded by whatever element they are. They have the ability to move through walls, and will approach knights at a very slow pace, They do not have physical attacks, instead move ever closer until they reach the same position of the knight inflicting elemental damage plus there status effect, They show a very weak resistance allowing even simple weapons to knock them back, Heavier weapons able to throw them away from you. When destroyed they display a simple implosion animation effecting near by team mates and enemys with the status effect and a low elemental damage. novas would be strong to Elemental, and weak to Shadow. The classifications are:
Nova - elemental + stun
Inferno Nova - elemental + fire
Venom Nova - elemental + poison
Frozen Nova - elemental + freeze
Static Nova - elemental + shock
Cursed Nova - elemental + curse, Graveyards Only
RARE: White Nova - elemental only, Invisible to players for the most part, visible only by a faint white mist, Becomes more visible as its damaged.. White Nova will not stalk knights like its cousins, Instead remains passive unless angered. When angered, a White Nova will move significant faster than standard Novas making it a tricky enemy to take down. Randomly spawns in place of any nova. Rare Drop chance for Nova shield which would feature as a invisible shield until blocking which displays a large mist.
The idea is that they would typically spawn just off-screen, and make there way in-screen during battle rooms.
This is pretty cool :DDD
Theyre kinda similar to the new drones and wisps, which makes it that much more probable that the devs will consider this ;)
But one suggestion: make the Novas not resistant to shadow (or neutral to everything, like drones and wisps), so they dont share too much traits with gremlins. But that's just my opinion <:{o (<-- moustache man w/ elf hat)