As with all of my ideas, this started simple and spiraled out of control. The first idea was "What if every boss blind was represented as a endgame boss blind?" And here's what I came up with for that.
The Hook - Discards all remaining cards when hand is played.
The Ox - If the most played hand is played, set hands to zero.
The House - None. There is no way for this boss blind to be made more powerful without changing it.
The Wall - Already represented.
The Wheel - 3 in 7 cards get drawn ace down.
The Arm - Decreases by 2 levels.
The Club and The Goad - Combined into one endgame boss blind called The Soul
The Window and The Head - Combined into The Heart
The Fish - None. Same reason as the house.
The Psychic - None.
The Water - None.
The Manacle - Hand size reduced to 5. (Hand size is -1 if it is below 5.)
The Eye - No repeat hand types this ante. (Keeps track of hand types played, similar to The Pillar)
The Mouth - None.
The Plant - None.
The Serpant - Draw 1 instead of 3.
The Pillar - None.
The Needle - Score requirement is 2x instead of 1x.
The Tooth - Lose $3, instantly lose if this can't be afforded.
The Flint - 1/4 instead of 1/2
The Mark - None.
Unfortunately I need to cut this inital message here for character limit.