Why Enemies Swarm or Thin Out in D2 Survivors (2026)

D2 Survivors, the free Diablo II–inspired browser game, doesn’t spawn enemies randomly — it follows a time-based population target that the update loop constantly tries to fill. Here’s the exact formula, read directly from the game’s own code, not a guess from watching gameplay.

Build verified: official macOS app 2026.1018.8 (2026-10-18). These are implementation values for this build; they shape what you’ll typically see, not an exact promise for every moment. See Act & Boss Timers for when the scripted elite/ring/swarm encounters land on top of this regular spawn pressure.

The population target

• Ordinary target population: 25 + 13 × elapsed minutes, capped at 390.
• While an Act boss or seal encounter is active, the target drops to 25 — this is why the screen clears out once a boss fight starts.
• Act I ramps in more gently: the target starts at 8 in the first minute, then interpolates up toward the normal curve through the second minute. Acts II–V use the full target from 0:00.

How enemies actually get spawned in

• A one-second batch timer adds extra quota — 1 + floor(elapsed minutes / 3) — whenever no boss/seal lock is active.
• In Act I, this extra quota is suppressed for the first 60 seconds; later Acts can use it from the start.
• Any quota that can’t be filled immediately (spawn debt) carries forward instead of being lost.
• Each update tries at most 8 spawn packs at a time, filling toward the current target plus that second’s quota, while respecting the hard cap below.
• A spawn can be deferred when the required monster animation isn’t ready yet, a local nest hits its limit, or the ranged-enemy cap (below) is already full.

The hard caps

The ranged cap ramps in on its own schedule in Act I: suppressed before 30 seconds, held at 2 through 60 seconds, then climbs toward the full ranged cap by 120 seconds. Later Acts use the ranged cap from the start.

Practical takeaways

• Standing still is the enemy of your own survivability. The scheduler keeps adding quota toward a growing target, so parking in one spot lets the population around you climb; moving to cleared ground resets the local pressure.
• The calm right before a boss isn’t luck. Target population dropping to 25 the moment a boss/seal activates is a scripted relief valve, not a lull you earned.
• Early Act I is deliberately softer. The slower ramp and suppressed ranged cap in the first minute give new characters breathing room; expect pressure to pick up noticeably around 1:00–2:00.
• Nightmare/Hell can change which monsters fill this pool, not the formula itself — see the Nightmare & Hell Difficulty guide.