Egg Chaser (Sonic Advance 3)

One of the hardest bosses in Sonic Advance 3 (and, indeed, one of the hardest bosses throughout the Sonic series), this battle sees Dr. Eggman chasing the player up a vertical shaft, populated by unsteady platforms that will fall just after touching them. As the battle moves up, this creates a bottomless pit, which is the biggest hazard of this fight. The only way to attack Eggman is to get the platforms to land on ontop of him, which is hard as he constantly moves back and forth. He also becomes invulnerable when he flips his machine over, firing a mace at the player. The best strategy is to worry about moving up without getting hit, as hitting Eggman will come easily; it is worth noting that if you get hit, unless you're lucky enough to land on another platform, you simply die. Fans tend to call this boss the "Egg Elevator", despite it not having an actual name.

Gemerl is situated just under the mace as Eggman flips over.