How about the Houndmaster in the Fort Joy dungeons?

Dragon Shane in Fort Joy
Djinn, Mordus, Lohar, Gorg, Marg, The Restless Scarecrow in reaper's coast

Act 1
Radeka The Witch, Migo, Trompdoy
Act 2
Mordus, The Advocate, Possibly the Natalie Bromhead encounter, Ryker, I think Xhaxh the lich, if it is possible to have his power grow if he is contued to be left alive and if you attack him after he spawns the chest he is at full power.

I will add more later

Late response, but thanks for the suggestions. Finally getting around to implementing more elites in the next update, using a script I created to scrape character data.

This data is available here in a spreadsheet, for those interested:
https://docs.google.com/spreadsheets/d/1q3sXKq39c12XKeKAYxVyCAvVgafnGcBHrqWn8oPyCzA/view#gid=0

^ Having all of this available in one spot makes it way easier to add elites to the game, as I can look up characters by name and find their ID to use within mod scripts.

Act 2:
-Murda (Drifwood Champion) or the Voidwoken in the Arena
-Lamenting Abomination
-Head Magister Knight hunting Hannag
-White Magister at the Oil machine
-Voidwoken Deepdweller at the electric frog fight
-Djinn
-Big Blackring guy around the Bloodmoon Isle tree (The Destroyer?)
-Harbinger of Doom
-Demons in Bloodmoon Isle locked cells
-Both Trolls
-Source masters (Ryker/Mordus/Jahan/Hannag/Almira/The Advocate)
-The Executioner
-Head white Lizard in the Red Prince ambush near Sadha
-Roost
-Alice
-The Lich
-Natalie Bromhead
-Mummy Dearest
-Paladin Thom Hardwin
-Aeteria
-Tovah
-Whichever White Magister is hanging Gwydian (changes depending on quest choices iirc)
-White Magister Vorrh (Mass shackles of pain guy)
---
Act 3:
-Black Ring Camp Leaders (Black Ring Captain, Wordless, Forktounge)
-Elven Scion
-Alexander
-The Great Guardian
-The Shadow Prince
-Knight of Duna
---
Act 4:
-Lord Kemm
-Toyseller Sanders
-Shadow Prince (if he appears act 4)
-Would it be too much to say Lucian, Dallis, and Braccus?
-Adramahlihk
-Isabella
-Queen Justinia
-Dorian Gall
-Brahmos
-Sanguine Tell
-Loic the Immaculate
-White Magister Reimond (If allowed to escape to Arx)

MajesticNoodle lähetti viestin:

Act 2:
-Murda (Drifwood Champion) or the Voidwoken in the Arena
-Lamenting Abomination
-Head Magister Knight hunting Hannag
-White Magister at the Oil machine
-Voidwoken Deepdweller at the electric frog fight
-Djinn
-Big Blackring guy around the Bloodmoon Isle tree (The Destroyer?)
-Harbinger of Doom
-Demons in Bloodmoon Isle locked cells
-Both Trolls
-Source masters (Ryker/Mordus/Jahan/Hannag/Almira/The Advocate)
-The Executioner
-Head white Lizard in the Red Prince ambush near Sadha
-Roost
-Alice
-The Lich
-Natalie Bromhead
-Mummy Dearest
-Paladin Thom Hardwin
-Aeteria
-Tovah
-Whichever White Magister is hanging Gwydian (changes depending on quest choices iirc)
-White Magister Vorrh (Mass shackles of pain guy)
---
Act 3:
-Black Ring Camp Leaders (Black Ring Captain, Wordless, Forktounge)
-Elven Scion
-Alexander
-The Great Guardian
-The Shadow Prince
-Knight of Duna
---
Act 4:
-Lord Kemm
-Toyseller Sanders
-Shadow Prince (if he appears act 4)
-Would it be too much to say Lucian, Dallis, and Braccus?
-Adramahlihk
-Isabella
-Queen Justinia
-Dorian Gall
-Brahmos
-Sanguine Tell
-Loic the Immaculate
-White Magister Reimond (If allowed to escape to Arx)

Is the author still active on this mod?

Would be real nice if the author did modify the mentioned enemies above for guarenteed elites!

I agree, would be nice for an update as this is way way better than the gift bag version which is just buggy and no fun.

Still active, yes. Been working on a pretty huge update. You can see the various steps of progress here:
https://github.com/LaughingLeader-DOS2-Mods/EnemyUpgradeOverhaul/commits/master

Expect guaranteed elites for every act of the game, new upgrades, script extender enhancements (making experience gained from enemies balanced to the highest player level, allowing you to play against higher enemy levels without gaining tons of experience points), and more.

Really glad you're still working on it and can't wait for the update :)
Hopefully this'll become the definitive difficulty mod as this game desperately needs a proper one.

Can't wait either :)
Are you considering the PHYS damage superiority in this new version?,

Sad to see the additional elites were not added but superb mod overall still

Is this ever getting an update? On a side-note, someone said that this mod scales enemies, but some friendly npcs might not necessarily scale and they get instakilled, is that still a thing and if so do you plan to address it?