Here's a small slice of the development progression I had gone through to design the 200' Sentinel Boss. A few of us were immersed for months on the Sentinel Boss Battle section of the game. I personally had a complete blast working on it from start to finish and am still very proud of all the fun, cinematic elements we were able to jam into it and how well it all came together in the end.
Final model render:
Here is the progression for the game's Elemental Boss - from thumbnails to final painted concept.
Machete Mutant (unused) with character-type explorations: