He claimed to have killed thirty or twenty in the Battle of Dirty Claw.
While the Fourth Doctor and K9 Mark II were helping Joe Bean and Babe Roth defend their cargo freighter the Spacehog from a Werelok attack, Brill scratched the Doctor. K9 then stunned Brill. The light reflected from High Sierra turned the Doctor into a Werelok. The Doctor entered the TARDIS and exited from time and space to find a cure, then returned.
On New Earth, Brill was imprisoned and hypnotised into thinking he was on the Doctor's side. He told the Doctor about his bosses, the Daleks. Brill, who knew about the Dalek battlecraft, joined the Doctor and K9 in boarding the ship. He killed several Werelox on board. Escaping the Daleks, the Doctor, Brill and K9 discovered the forbidden Room of Many Centuries. They ran back to the TARDIS, Brill quickly dispatching the guards, and materialised inside the Room of Many Centuries. K9 and Brill cleared the room of Daleks, and the Doctor disconnected the time-space rationaliser of the time transporter, freezing the Daleks in one moment in space and time forever.