This mod should allow you to possess all ranks.

At the highest level of the Possess talent, it enables you to possess any rank of enemy, including Elite Bosses.

I recommend the excellent Proper Possession, as well.

More Boss!
This addon introduce 8 new bosses to the game, with their different fighting styles and special abilities.
You will see the detailed introduction about those bosses and their special abilities in the forum post.
This addon is still in Alpha test, so it is expected to have many bugs and really unbalanced settings. Hope to hear your feedbacks!

Adds 3 new dungeons to the world map (blood soaked ruins, infested ruins & wolfmire) these dungeons will have unique boss and lore spawns. 8 new bosses have been added that will spawn in the new dungeons (they will also spawn in Infinite Dungeon)

Over time I will be adding more dungeons to explore and bosses to defeat! I also have plans to create new mobs and mob variations, create unique artifacts and eventually implement a quest system to reward you for defeating the new bosses (since quests are not yet implemented bosses will drop gold upon death.

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IMPORTANT: I am unable to respond to comments on this site as my comments keep getting blocked as spam! If you have issues/bugs/requests you will need to post your comment on the STEAM Workshop addon page here: https://steamcommunity.com/sharedfiles/filedetails/?id=1769451307 So I can see/respond to you there.
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Colorizing unique+ ranked creatures on minimap

Originally separate addons by Starkeep, I take no credit for his work and spliced these two addons only to see if I can do it, and so I can tweak some numbers without my save getting invalidated. Again, all credit for the main addon body all goes to StarKeep. I merely spliced the addon together for my amusement and convenience.

Allows the player to pick multiple classes, as well as giving the option to spawn rares and randbosses, and control loot quality and spawn rate. Added a setting for the experience penalty from MultiClass Challenge.

In order to activate this addon, go to your Game Options for a new tab.

Allows the player to pick multiple classes, turning all enemies into Randbosses as a counter-measure.

In order to activate this addon, look at your Game Options for a new tab.
EXP penalty you suffer from using this addon has been modified, from 0.5 to 0.85 (You only lose 15% EXP now)
Original Author is StarKeep, all credits go to him, I do not take credit for any of his work, I only modified the EXP penalty. - Rae
Updated Version 1.4.1:
- Possessor and Adventurer can now be chosen in the Multiclass menu

Allows the player to pick multiple classes, turning all enemies into Randbosses as a counter-measure.

In order to activate this addon, check your Game Options for a new tab.

Massively spikes Rare counts as the game progresses, and even adds in Randbosses in the late game.

As of 1.4.2, the player can fully control the spawn rate of Rare and Randboss class enemies to suit their gameplay style.

A fork of Everything is Unique. Its broken. Use Randboss Rando instead. https://te4.org/games/addons/tome/randboss_rando