Green Demons.
The only thing known about Green Demons is that their overall power levels are
600 to 900. The individual stats that actually matter (magic, strength and spirit) are completely unknown. The same could be actually be said for other any lesser Demon in the series, but they have actual feats and scaling to get some idea of how powerful they truly are (plus, they're about to play a pretty big part in current NNT revisions).
Their only appearance where they actually do something of note is
chapter 233, where they run past Arthur and threaten Chimera Orlondi (who's featless). The only other appearance
in general is chapter 259, when
they're about to get fired on,
half-obscured by the panel and about to
get drowned by Diane. Green Demons appear so little that you don't even see their corpses in battle scenes.
They don't even use flight, soul manipulation, darkness or hellblaze like every other demon.
Basically, they have no feats, no useful scaling or statements of any kind, no on-screen abilities aside from Superhuman Physical Characteristics, and they appear for 5 panels across 2 chapters in a 346 chapter manga. Calmadios had more reason to exist, and we
axed that profile.