I have significant experience with boss battle design, designing over 30 unique boss encounters over 5 different titles.  The following section highlights some of the bosses I have worked on over the years. 

TIE fighter & TIE bomber

These are two separate boss encounters that take place at various points in Star Wars Rebels.  I pitched the concept around having the player battle at Tie Fighter early on in the preproduction.  I wanted to do this for several reasons:  

• TIE fighter offered the player an iconic and oh-wow moment
• The level would take place in an elevated location.  From a production standpoint, this would reduce the the artists to create a dense level.  We could rely on minimal level blocking mostly focusing relying on the skybox.  
• A TIE fighter model was already provisioned for use as a level prop. Since TIE fighters have very little articulation, animations production was minimized. 
• We could easily turn this into two separate battles by using a TIE bomber model.  We achieved a second and unique encounter by simply added an additional attack pattern and dropping in a new mesh.  To add further escalation and challenge, the level platforms were also reduced. 
• We ended up also reused the strafing pattern of the TIE fighter as a level hazard in a few of the levels.  This was a nice win and allowed us to stretch the game content further.

Footage of the TIE bomber battle:

Our production partners were concerned about the scale and the blocking of the level.  The patterns assumed that the TIE fighter would hover in place.  This was not an issue as we cited canon source material that indicated TIE fighters can hover in place.  You see this in Star Wars Rebels as well as Episode 7.

Trap Jaw (He-Man)

He-man bosses, used a theme first approach to design.  Key traits of the boss characters were amplified.  Since the physical rules of the world were very loose, we could get away with creating some very unique and funny set ups.  Trap Jaw was a master of machines, but awkward in nature. These traits were distilled and reflected in a machine that is piloted from inside the wrecking ball.

We were on a bit of a budget, but I also wanted to introduce some variation in boss battles. We have had several bi-pedal boss battles already and running animations were expensive to produce.   The design solution required very few unique sprites. Most of the animations were derived by translating/rotating pieces of a single sprite. The solution also produced a very unique and over-the-top boss encounter. 

Here is a video of the Trap Jaw battle in action:

Master Mold (X-Men)

Giant Spider (Star Marine)

Mer-Man (He-Man)

I wanted each boss battle to end with a humorous finale.  Here are some some examples of the funny things that happen to each of Skeletor's minions.  I was especially happy with the Hordak and Beast Man finale.