The Elemental Baron was one of the first concepts made for the channel, and as such it tends to have a few aspects about the design that don't resonate with how I view the experience of Doom Eternal today.
Regardless, the original vision for this demon was to diversify the super heavy demons for the late game of Doom Eternal by introducing a new mechanic, elements. This concept of elements in Doom Eternal would later be revisited and slightly tweaked in my Elemental Spirit concept which took this idea and expanded it to virtually every other demon.
I've been on record to say many times that my primary goal is to make Doom Eternal more interesting, more replayable, more fun. While I agree with my past self that the Elemental Baron would make the game more interesting and replayable, I'm not certain about fun.
The elements were:
Fire
Ice
Energy
Poison
And each would inflict a lingering ailment on the player. Generally speaking, Doom is the most fun when the player is in control and winning. It's not fun when you're slowed down, overwhelmed or needing to handle multiple bullet sponges. Unfortunately, this concept is one that a demon might perfer to a player as it actually gives them an advantage. Perhaps in hindsight, this would be brilliant for a master level but those got scrapped along with many other aspects of the game.