The Boots of Speed is an artifact from Hexen.

Boots of Speed

When a player uses them, they will run at twice their normal speed, and also leave behind afterimages of the character that the player is using. Curiously, if the mage is moving using the Boots of Speed, the Frost Shards projectiles may damage the mage instead of firing outward.

With the vanilla Hexen engine, the afterimages could be seen by running backwards, but they cannot be seen in ZDoom unless in chasecam mode.

Hexen items
Health Crystal Vial | Quartz Flask | Mystic Urn
Armor Amulet of Warding | Dragonskin Bracers | Falcon Shield | Mesh Armor | Platinum Helm
Artifacts Banishment Device | Boots of Speed | Chaos Device | Dark Servant | Disc of Repulsion | Dragonskin Bracers | Fléchette | Icon of the Defender | Krater of Might | Mystic Ambit Incant | Mystic Urn | Porkalator | Quartz Flask | Torch | Wings of Wrath
Others Ammo | Keys | Puzzle Artifacts