Sith Abomination

In Terms of the Heroes
The heroes first caught wind of the Sith abomination program when they discovered a Jedi smuggling operation on Nar Shaddaa, though at the time there wasn't much evidence to lead them to the conclusion that the Jedi prisoners were being used for abominations.

The heroes encountered their first abomination on Dantooine, in an encounter with Darth Phil over recovering the Jedi Enclave's archives. This abomination was none other than a Jedi Master they had previously adventured with, Master Kessel.

The heroes eventually traveled to Katarr, the home of Darth Homunculus, and the Sith's greatest contributor to their abominations. There they saw the massive prisons housing hundreds of Jedi and thousands of other life forms, and laboratories filled with row after row of vats containing half-formed abominations. There, they also encountered Tin, Saren's force sensitive brother, who had been transformed into an abomination that seems unkillable.