After Darth Sidious became aware of how powerful Count Dooku's apprentice Asajj Ventress had become, he ordered Dooku to have the aspiring Sith Lord killed. Asajj escaped however, and returned to her people. Mother Talzin welcomed Asajj back, and offered to assist her in getting revenge on Dooku. First Asajj and a pair of Nightsisters using a spell provided by Talzin to render them invisible attempted to assassinate Dooku, when that failed Talzin provided Asajj with an ally, the Zabrak Nightbrother Savage Opress, who Mother Talzin offered to Dooku as a new apprentice when in reality he was a sleeper agent for the Nightsisters.
Count Dooku became aware of Talzin's treachery and sent General Grievous to exterminate the Nightsisters, Talzin was among those killed.
It has also been revealed Talzin was the one who saved Darth Maul after his dual with Qui-Gon Jinn and Obi-Wan Kenobi on Naboo.