Classes:PlayerSpeedTrail

From ZDoom Wiki

Player speed trail
Actor type	SFX	Game
DoomEd Number	None	Class Name	PlayerSpeedTrail

Classes: PlayerSpeedTrail

The trail of after-images left by a player using the boots of speed or equivalent power. They gradually fade out in seven tics, becoming more and more translucent every tic, and are destroyed at the eighth tic. The actor can only be seen in chasecam, by other players and cameras but never by creator's point of view.

DECORATE definition

ACTOR PlayerSpeedTrail native
{
  +NOBLOCKMAP
  +MF_NOGRAVITY
  RenderStyle Translucent
  Alpha 0.6 // This value is decreased by 0.075 every tic, and the
            // actor destroyed after it reaches 0.075 or below.
}