The insertion is quite difficult due to using UberASM and there are many stuff to consider (though that shouldn't be surprising for you).
And it also would have been nice if there were an easier way to get the subroutines for the patch and that you can disable the HP display for chuck when you have allowed the patch before.
Bug found: ludwig boss has an HP underflow glitch where if you get his HP down to 5, and stomp on him on midair (1 HP left) (about halfway on his jump animation when he is able to be stomped), and shoot 2 fireballs on the frame he ends his "stomped animation", his HP will decrement TWICE (both fireballs absorbed) and ends up with 255 HP while dying. I recommend not having fireballs or not having the ludwig boss altogether until I'll update the patch.
Edit1: Fix another glitch where if the damage is large enough to exceed 255, will overflow (without death). Fixed by checking if the value goes over 255 via BCS after the ADC.
Edit2: Really optimized the damage subroutine code (only used by custom sprites), after learning that if the SBC underflows a value, the carry clears, it makes the CMP redundant.
New bug found: When a chargin chuck dies by falling off screen, SwitchHPBar will be executed every frame until its sprite status ($7E14C8 = #$00, when it goes far enough below the screen), causing the HP bar to instantly switch back to the dying enemy when the player attacks a different enemy, also freezing the record damage indicator should $9D is frozen while the enemy is dying. NOTE: I'll update this patch once my new graphical bar gets done updating.