Bacterium Prime is a new boss in Exxo Avalon. It is the boss for the Contagion, a new biome.
Its stats are as follows:
1500 Max HP
Completely knockback resistant
In stage 1, Bacterium Prime will act similarly to the Brain of Cthulhu. It will send minions after the player. However, if you hit the main body of the boss, it will increase a counter variable, and if that hits 12, it will spawn another minion. The boss is immune to damage in this phase.
In stage 2, its eye will open and the boss will get faster. It has 1500 HP in this phase, making it quite an easy target.