Tarnished forgotten primarily controls the soul and does little damage, they cap in hp at 2 soul hearts.
HERES WHERE THE FUN PART IS
Tarnished forgotten has a pocket active called something like "Pulsing Femur"
When it is used, The skeleton of tarnished forgotten will appear in the room, and the soul can enter it like a shell, It can take 5 hits, looks like a bigger, more broken version of normal forgotten. When the shell is broken, The soul will exit the skeleton, and the skeleton will fight alongside the soul with similar ai to a minisaac.

Instead of tarnished forgotten having a dead weight, like tainted forgotten, he has a dead bodyguard.