All boss monsters have multiple counters. The one counter all bosses share though is the Boss Timer. It's a skill that has a 100% chance of casting whenever a boss is struck. It basically causes the boss to curse itself. A small red pulsing overlay will appear over the boss's head (the graphic overlay for the curse) once the Boss Timer is triggered. The Boss Timer curse does not interfere with other curses and lasts for 20 seconds after the most recent boss timer triggering hit. While there are ways to damage a boss without triggering any counters the skills that can perform it have been greatly reduced in number due to the efforts of the modder. The instant the curse ends, however, the boss will start healing at a massive rate and the mod Prevent Monster Heal and poison will not stop it. This Boss Timer counter combined with the removal of town portal scrolls is intended to force a group of players to fight and finish off a boss in one sitting or else the boss will return to full health wasting their efforts.

A number of bosses on their death create a portal to a special area with a death counter. Thorns damage has been infamous for killing portal spawning bosses without spawning portals (Thorns damage kills monsters without triggering their on death counters).