Each removable parasite should strike a balance between being difficult enough to not be practical to remove until the player knows the cure, and not being apparently impossible to remove before that.
The first round of balancing is just the basics:
[x] Balance cuttability for all parasites. Soft parasites are difficult to cut and hard parasites are easier to cut (but might have more durability). Some parasites should be impossible to cut as they're e.g. inside the player.
[x] Balance Phys and Mag resistances for each one. Doing it by the Spice Girl principle makes the most sense - soft parasites resist physical but hate magic, while hard parasites are the exact opposite. Some may not need these at all, as they would use the plug minigame and not the struggle.
[x] Add regeneration to every parasite in appropriate amounts.
[ ] Look into changing regeneration rate based on various events
[x] Trim DD holdover stats
[ ] Test all of the above to ensure it's practically impossible without a cure, and quite doable with a cure.
Each removable parasite should strike a balance between being difficult enough to not be practical to remove until the player knows the cure, and not being apparently impossible to remove before that.
The first round of balancing is just the basics: