Stan revealed the Clan's prophecy about the Chosen One. If the Chosen One died without fulfilling their prophecy, the Clan's temple under Blood Gulch would fail and the long-range jammer would be deactivated. When the canyon decided that Ziggy was the Chosen One, Stan brought a crew of humans as well as Ziggy to the temple. He sampled a finger of Ziggy's to the temple's core, but the sacrifice was rejected. That's when Stan knew Ziggy was not the Chosen One, and figured out it was himself.
Stan died sacrificing himself to the temple, destroying the prophecy and effectively crippling the Clan and giving Blood Gulch long-range communications again.