Sash and Waistcoat were two of three unmen created by Ixidor in Otaria on Dominaria. They were known as troublemakers.
Un-men are basically living portals that let the dementia caster teleport in case of emergency. They seal themselves and basically die when someone passes through them. Sash and Waistcoat did not want to die for Ixidor, so they left. For a while they gained bodies of cockroaches, a gift from the Cabal Patriarch. Then they eventually got new human bodies but sustained wounds by walking naked across the blistering sands of the desert. They were found and healed by Karona, who ended up befriending them because they were not affected by her aura and didn't worship her. After some time, Karona decided that they could help her discover her true identity, so she took them as her disciples.
When Sash came to the conclusion that Karona was magic manifest, she instantly took on the idea and started to test her newfound powers. Through much trial and error, they discovered that her powers were based on faith. After Karona's power began to rise out of control, she attacked the Numena and killed many people. In the end Kamahl came to bring an end to Karona's reign but he almost lost the fight. Acting under advice from Lord Macht, Sash and Waistcoast then betrayed Karona, and pierced her belly with the Mirari Sword.