This entity is obsolete; its use is discouraged and it may only exist/function in older engine branches.
This entity is not in the FGD by default.
It should not be put directly in a map.
_plasma is a point entity available in all Source games. This is the effect that is created from an env_fire when using the Plasma type of flame. The effect appears to have never been created.
In code, it is represented by class CPlasma, defined in plasma.cpp.