Oh, shut up and help me remodel the Sergeant Sapp page!
He is first seen when Yew Geneolgia and Edea Lee set out to revive Tiz Arrior, ruthlessly ordering an army of Imperial soldiers (including Private Piddler) to kill any Eternian they see, whether they're a soldier or citizen.
They appear once again in Eisenberg piloting the Superd'nought Baël (shortly after the defeat of Angelo), though they arrived a few days late. The Sergeant makes the decision to destroy Hartschild, but Yew's party stopped them by defeating them in battle. Sapp and Piddler then receive a message from the Empire, informing them to immediately return to the Skyhold or be left behind, as well as ordering them to prevent the Baël from falling into enemy hands, with the punishment for failure being a court martial and execution via firing squad. Sapp then orders Piddler to pull the machine's self-destruct lever, but it broke off during the battle. The duo then drive the Baël back to headquarters.
The soldiers encounter Yew's party one last time in the Temple of Water. Apparently, immediately after returning from Eisenberg, the Empire strapped the two to the back of the self-piloting Vucub Caquix before deploying it. The machine then fights against Yew's party immediately after the Water Crystal was overloaded; however, the machine was destroyed.
Sapp and Piddler managed to survive the battle, with the Private replying to Nikolai comments on the robot's destruction, saying he "brought plenty of copper tents this time." Their whereabouts afterwards (as well as in the second timeloop) remain unknown, and so does whether or not they survived longer than that.
"Sapp & Piddler's Theme" plays during any scenes involving Sergeant Sapp and Private Piddler, as well as the battles against the Superd'nought Baël and the Vucub Caquix.