The dwarf engineer's daughter, revealed to be a fabrication — the reason he chose to die.
Tizquick stayed aboard The Nightmare Express to detonate it in The Abyss, telling Carl not to worry, that he knew how this worked and would make her blow nice and big just before they hit the bottom of the pit. Standing in the empty trainyard afterward, Carl set out the two deaths side by side: Fire Brandy had killed herself to save herself from losing more children, and Tizquick had killed himself because his daughter had been a lie.
Never seen; she did not exist.
The fabricated attachment used to control Tizquick, and the discovery that unmade him.