Infected Creepers are mobs that start out extremely rare, then get progressively more common as the Player plays more and more in their world. For about every 10 hours played in one world, the chance of an Infected Creeper to spawn goes up by 1%. This means that it would take 1,000 hours in one world for an Infected Creeper to have a 100% spawn rate.
Infected Creepers are very dangerous to fight. They behave like zombies, however, they move twice as fast as the player and have a chance to inflict Infect on the player when they are hit. Infect causes the Player's screen to be a red hue and swirl around in Nausea VI, and their movements are reversed while they slowly take damage. It is not cured in any way, and armour does not affect the damage received. Infected Creepers have 40 <3 (80 health), but their weakness is Angelic blades. When killed, they drop 1-3 Tentacles and 0-2 Gunpowder, and a friendly creeper will spawn in the Infected Creeper's place when it is killed.
Infected Creepers spawn anywhere and have a starting percentage of 0. Once the player spends more time in their world, they will spawn in any biome around every 20 x 20 area of blocks. They spawn also in every dimension except The Moongardens.