In its first stage, the Derpking will spawn 1-3 Derplings at once, replacing them if they die. It will bounce around, trying to hit the player.
The second stage of the fight is activated if the Derpking falls to 3000 . He will jump much higher in this stage, and spawn Derplings every time he lands from an especially high jump. In addition, he will begin lobbing small blue spheres at the player. If the player dies to these, the death message will say "Player got an overload of derpiness."