Lost Soul limit

To prevent overloading the engine with Lost Souls, a hard-coded Lost Soul limit was added which prevents Pain Elementals from spawning them if there are already 21 Lost Souls in the level. Because the Pain Elemental has no other attacks, this has the side effect of rendering them helpless when the limit is reached.

This limit is removed in some source ports. In Boom and its close derivatives, the limit may be toggled as a compatibility option.

Hell Revealed's MAP19: Everything Dies utilizes the limit to create a trap at the beginning of the level. The player starts inside a room with a megasphere in the middle, and four Pain Elementals, rendered harmless by the presence of 36 Lost Souls in an inaccessible room. Grabbing the megasphere, however, will cause all of the Lost Souls to be crushed, allowing the Pain Elementals to attack you.