Every entity, regardless if it possesses specific outputs, can be used to fire a sequence of events via the FireUser input. The FireUser input can be related to a subroutine. FireUser inputs are useful for complex entity setups that can be triggered multiple times in a cascading fashion.

In the example map provided, there is a env_explosion entity parented (attached) to a prop_physics garden gnome. There is a point_teleport entity that teleports the garden gnome on the pedestal behind the glass. There is a trigger_multiple entity behind the button that controls and teleports the gnome to the pedestal and fires a series of explosions to bounce the gnome around the room. Since the env_explosion entity is parented to the gnome, wherever the gnome is, the env_explosion entity is in the same relative position. The button on the post tells the trigger to use FireUser1, and the trigger_multiple entity activates all the outputs relative to the User1 input.

Now, any other entity...