Pre-Hardmode bosses[edit | edit source]
Bacterium Prime is a large, flying bacteria with 1,500 health. It awakens after every third Snot Orb that is broken or after a Infested Carcass is used. Snot Orbs are found in the Contagion's chasms, surrounded by Chunkstone, which requires a pickaxe with 60% pickaxe power or higher to mine, although explosives or Purification Powder can be used to bypass this. Once within range, Snot Orbs can be destroyed with a hammer or explosives. Bacterium Prime can only be summoned in the Contagion, but at any time of day.
Bacterium Prime has two forms. In the first form, it can be hit, though any attacks will not inflict damage, and Bactus Minions will float around it. After all of these are killed, Bacterium Prime will go into its second form, where it will teleport more frantically and move a lot faster, so a ranged weapon may be needed. Bacterium Prime's second attack form is ramming, like the second form of Eye of Cthulhu. Unlike most other bosses, Bacterium is not immune to knockback.
Bacterium Prime is the only source of Boogers in the game (other than the bactus minions spawned while fighting it), and drops a large amount of Baccilite Ore, which are their equivalents to the corruption items Shadow Scale and Demonite Ore, and the crimson items Tissue Sample and Crimtane Ore respectively.