Diamond of Pantheos
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 the episode "200" to revive her.
It was also planned to make an appearance in South Park: The Stick of Truth, as it was hinted in the preview, but was cut due to the game's extensive plot. It would've been used by Clyde when attacking the main boys.
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. At the end of Mecha-Streisand, Ike finds it and grows giant.
The Triangle of Krewluck
Barbra Streisand had already found the other half of the Diamond of Pantheos, the Triangle of Krewluck. She kept it in her mansion. This other half was light blue, in contrast to the Triangle of Zinthar's yellow color.