The disease in Harran isn’t lying dormant while people run around trying to survive. It’s constantly mutating and creating stronger monsters. In the beginning of the game, you won’t find many dangerous Infected, but things get harder out there as the story progresses.
The following chart shows you when various Infected begin to appear throughout the city.
| Mission | Possible Enemies |
|---|---|
| Awakening and First Assignment | Biters, Volatiles, ˆ’ Melee Thugs |
| Airdrop | Goons and Virals |
| A Pact With Rais | Gas Tanks, Toads, and Bombers |
| Hunt Your First Bolter | Bolters |
| The Pit | Demolishers, Rais’ Ranged Thugs |
| Project Mayhem | Screamers |
| Contact | Expect Anything and Everything! |
This isn’t the only way in which the difficulty rises over time. Enemies become stronger even within their own categories. There are three or four tiers of Infected within each category. The Biters that you attack right outside of the Tower on day 1 are not going to have the same stats at the ones you meet toward the end of the game. This doesn’t happen as a major switchover. Instead, the Infected have percentage chances to appear as tougher versions of themselves. Those chances increase dramatically each time you finish a major story mission.
None of this is influenced by Kyle’s XP, weaponry, or time in the game. If you want to keep the difficulty lower for as long as possible, complete side quests and challenges before advancing the main story.