From Valve Developer Community
This entity is not in the game by default, but got left over in the FGD.
Boss Battle Entity. This is used to detect a Boss Battle map.
- Removes this entity from the world.
- Removes this entity and all its children from the world.
- Evaluates a keyvalue/output on this entity. It can be potentially very dangerous, use with care.
<output name> <targetname>:<inputname>:<parameter>:<delay>:<max times to fire, -1 means infinite>
- Fire the
OnUseroutputs; see User Inputs and Outputs.
- These Outputs each fire in response to the firing of the like-numbered
FireUser4Input; see User Inputs and Outputs.