@HeadgeCactus
Thanks for the reply. I've mentioned in a previous post that I've been trying out the mod with a weapon pack and I've found that the additional enemies are much more fun to fight so HP nerfs don't concern me as much, although some could still use some tweaks with their abilities. I also like that Blue Spider Demon you've shown off and since we are on the topic of new sprites I've got even more suggestions. I did some quick editing in gimp so the images below might not look perfect, and I didn't even edit the whole sprites, I just wanted to give a basic visual of my suggestions.
The suggestions below are mostly visual, if I do have ideas for behavioral changes than I'll list them along with the image

Sources
All from the realm 667 repository (except for the purple zombie), the Fireblue zombie is from the heretic style

White shotgunner (Zardaz) abilities: I'd keep it's speed and attack patterns similar but replace the exploding shotguns and have him fire fast moving projectiles rather than a hitscan barrage.
sources:
green - yellow, realm667 repository (Doom Style), Cyan, Fireblue & White from realm667 repository (Heretic style)

New abillities:
White Chaingunner (Banshee) - her overall behavior and attack patterns won't differ much from the mad scientist, the minions she summons however will.
Banshee Minions - Night Shade (Imp level flying enemy), Lost Spirit (ghostly enemy that can pass through walls and fire projectiles), Spirit Imp (ghostly imp that fires a homing projectile, upon death they release a docile wondering ghost that can sacrifice itself to resurrect fallen enemies)
Sources - all from the realm667 repository, both Doom & Heretic styles

Blue Imp may not look very blue here. A blue tint will likely need to be added with the partial invisibility effect.
Sources:
All but the nightmare Imp comes from realm667 (Doom Style), the nightmare imp is from Doom 64

Gray demon abilities - The abilities that the stone demon comes with are already pretty good and fit in well with the stone like aesthetic of most of your gray enemies
Sentinel - Overall I think it should function the same way as the robot but have it replaced with a more demonic looking enemy, the guarding cubes will surround the Grand Sentinel rather than tiny spherical robots.
Gargoyle swarm - Meant to as an alternative to the bees, they can still function the same way, just replace the bees with a monster that better fits doom
Sources:
Satyr, Stone Demon - realm667 (Doom Style), Gargoyle - Realm667 (heretic/hexen style)
Blue Pain Elemental - Doom64
Sentinel, guardian cube - Hellforged

sources:
blue caco - hellforged
purple caco - Doom 64

sources:
Purple Rev - Hellforged

sources:
green, arachnophytes, arachnorbs - realm667 (doom style)
Blue spider - Doom 64
Brown spider - Hellforged

White Mancubus abilities: I think it could keep the attacks from the greater incubus as they are already powerful. I suggest adding in the ability for the Inkubus to melt itself into the ground and reform itself elsewhere (hens the name Inkubus). The melting ability could be used to surprise the player or retreat when wounded.
Source:
Blue, cyan, fireblue, and white all come from realm667 (Doom, heretic, and other styles)
Purple, & brown - Hellforged
Green - I got this one from a monster expansion for Brutal Doom, it may have come from project brutality originally but I'm not sure of the exact source.

I wanted to have one for purple but I couldn't find a fitting sprite for it
Sources - realm667 repository (doom style)

In hindsight I feel I could have made the armor on the blue guy pop a bit more
sources:
green & blue - realm667 (heretic/hexen style), Afrite - realm667 (Doom style)

White Baron abilities (Baron of Time): My suggestions for the Baron of time are heavily inspired by the Time Imp from realm667, I suggest testing him out so you can get a feel of what I'm going for with the white baron.
Health: 8000
Basic attacks: much like the barons attacks but faster and more damaging
Slow Time: The Time baron slows down time for everything on the map but him, this lasts for 30 seconds
Stop Time: time is force to freeze entirely, this effects everything on the map but the baron, lasts for 3 seconds. This ability is often used to trap the player so he can be pelted by the baron's fireballs
Time Travel: upon death the barons soul will leave it's body and return after a short time (about 25 seconds?). When in this second phase the Time baron will have double the speed but half the hitpoints.
Sources - all from realm667 (doom style)

Hell mother abilities:
I think the hell mother (white spiderdemon) should be a powerful summoner, spawning large amounts of demons to attack the player, think of her as a miniature and more mobile Icon of Sin. The hell mother prefers to keep her distance and not engage the player directly but if push comes to shove she is very capable of defending herself with powerful projectile attacks. I'd put her health at about 12000
Sources:
purple - Hellforged
Fireblue - Realm667 (doom style)
White - While it's based on the motherdemon from doom64 I used an altered sprite from Brutal Doom

White abilities - I'd keep it's attack patterns similar to the white cyberdemon that's already ingame, although maybe not have it launch itself in the air as that ability may look rather silly with the new sprite.
Sources:
green, purple, fireblue, red - Realm667 (Doom Style)
blue & black - hellforged
white - edited version of Korax from Heretic