Custom Powerup
From Halopedia, the Halo wiki
The Custom Powerup is an object in Halo 3, similar to the Active Camouflage and the Overshield.
Overview
This object can only be placed on maps by using Forge. What it does is decided by a player when setting up a custom gametype. It can affect many player attributes, such as damage resistance, gravity, damage, etc., including multiple simultaneous effects. It can make a player an "instant Juggernaut", or even negatively affect a player. It will appear as a floating yellow orb. [1]
