DER is a fork of AID, but they are fundamentally different: The purpose of DER is to supplement the enemy spawns of a map, whereas AID replaces them entirely. DER simply adds enemies, regardless of player health, and it never changes items.
DER has 4 pairs of CVars that control how often reinforcements are spawned, how close they are to the player, and the severity. Each pair is the minimum and maximum of the range for generating random numbers. Thus, by default, DER spawns 1 to 3 groups every 15 to 45 seconds, and each group has 2 to 4 enemies. They will teleport in, sometimes very close to the player.
The enemies hand-placed by the map designer are the starting pool for randomly spawning reinforcements. However, the roster is not created until the 3rd map tick, after other enemy mods may have altered the pool. Thus DER should work seamlessly with other enemy mods.
Disclaimer: The default settings can be intense. Reinforcements will spawn very close to you. I've had jump scares
