Perhaps an idea for a whole other mod (or a configuration option)

As usual you would get to mines 2 to acquire the knife piece 2, it would spawn on a pedestal and taking it would spawn mother shadow as usual starting the escape, HOWEVER
Taking the piece would also spawn a door to a boss fight... THE THING THOUGH IS

> While fighting the boss, mother shadow would still chase you >:D and insta kill you if it hits you.
> To compensate this, you can make the item from devil/angel pool or force it to be a Q3/Q4 item.
> Otherwise you can make it 2 boss fights, the 1st room is a normal boss while having to avoid mother shadow with a normal boss item as a reward, a 2nd door to another boss fight would spawn where you'll have to defeat mother shadow her/itself which would grand you a special item AND make the "escape" easier.

Since acquiring piece 1 would give you the opportunity to get a boss item, I thought why not having something similar for knife piece 2.

waddayasaym8