need help with damage balancing

so Zarby released a damage property editor that works against enemies and combined with superskuj's sprite editor, many unkillable enemies can be destroyed. my question is though, which items should be edited to destroy the naturally indestructible?

Depends a lot on item progression really. Already the original has several enemies that are "nearly indestructible" and require an item that comes up soon after or shortly before they first make an appearence:
– red cyclops/mimics: arrows
– turtles: hammer
– ice elementals: fire rod
– centaurs: lvl4 sword / silver arrows
So you could use this to create "meat gates" in dungeons, a la room 1 of Ice Palace.

(Consider also the possibility of beefing up some other enemies to be newly indestructible.)