The combat robe bottom is a reward that can be purchased with tokens from the Fist of Guthix minigame. It degrades with use similar to the Barrows equipment, and may only be traded when completely degraded. It requires level 20 Defence and level 20 Magic to wear, and is the lowest-level PvP armour for the legs slot.
Similar to all other armours obtained from the Fist of Guthix minigame, it can be degraded for trading purposes by talking to Reggie in the cave and asking him to degrade the item. This item costs 10 Fist of Guthix tokens to recharge.
By itself, the bottom does not grant any special effects, but wearing a full set of robes, there is a 5% chance that the robes will supply runes used when casting a combat spell. Any mind, chaos, death, or blood runes used during combat is replenished.