The Diamond of Pantheos is a relic made up of two triangles: the Triangle of Zinthar and the Triangle of Krewluck. Both triangles are needed to form the Diamond, which has the power to transform Barbra Streisand into Mecha-Streisand, a giant mechanical version of herself. It appeared in the episode "Mecha-Streisand" and again used by the celebrities in episode "200" to revive her.
The Triangle of Zinthar
The Triangle of Zinthar appeared in the episode "Mecha-Streisand"; in which Barbra Streisand needed to get two triangles (Zinthar [yellow] and Krewluck [light blue]), the other one being the "Diamond of Pantheos" to become Mecha-Streisand, who also featured in "200". She re-appears in that episode and decides to help the other celebrities in destroying South Park. The artifact was uncovered by the children while on a school archeology field trip. Originally thought to be an arrowhead from ancient times left by a local tribe, Pip was the first to find it and pick it up. Cartman steals it from Pip out of greed.