What Is An Eggshell Top?
Basically a seashell top, but with egg-shaped "shells" and the color and texture of ivory. This is an Enchanted item of clothing worn mostly by mermaids and Dancers; both prefer to wear less clothing, and this item enables that by granting 'durability like unto a Chomper' for the wearer.
By durability 'like unto a Chomper,' I mean an Eggshell Top enhances the wearer's durability to mimic that of a Chomper. Inside their enamel shell, Chompers are made of a thick jelly, almost as firm as rubber cement (dents when struck by a hammer but does not permanently malform), and so an Eggshell Top causes the wearer to get an increase in durability proportional to the difference in durability between a shelled an unshelled Chomper.
To be more specific, a Dancer wearing an Eggshell Top won't be pierced or bruised if someone attempts to stab her with a dagger, and will be unharmed by punches, falls (I'm not talking falls from cliffs and buildings, merely tripping or falling out an average-sized tree), kicks and so forth. Stabs and slashes will be ineffective, but bludgeoning weapons (maces, axes, warhammers, picks) can and will penetrate these enhanced defenses.
Cool Enchantment, bro! What's the problem?
The trouble is how the Enchantment works; it gives durability like a Chomper to the wearer, right? However, this provides an easy exploit for adventurers. Since, by definition, the wearer possesses the durability of a Chomper, and adventurers can increase their Fortitude (willpower, endurance, vitality, and durability) as they Level Up, this means the wearer can Level Up their enhanced fortitude and thereby achieve unnaturally high Fortitude.
This is bad because with Fortitude maxed, an adventurer is immune to conventional weapon attacks. In more precise terms, one needs high-end gear to harm an adventurer with max Fortitude, like an adamant sword or mithril mace.
Assuming an adventurer buys and equips an Eggshell Top at Level 1, and assuming both A) that one's base Fortitude is multiplied by 1.01 with each Level Up and B) a regular person's Fortitude at Level 1, wearing an Eggshell Top, is a nice 6 or 7 out of 10 (with 5 being average and 10 being the maximum possible limit), it becomes even more clear how bad this is:
Max Level: 500
Normal Person's Maximum Fortitude At Max Level: 725
Eggshell Top Wearer's MFaML: 870-1015
My question is simple: How Can Eggshell Tops Be Balanced?
I have an idea for a possible solution (placed below), but can't figure out how to make it work. I'm open to other ideas, however, and will appreciate all input.
Stagnant Shielding-Perhaps the degree to which Eggshell Tops increase one's durability A) never changes and B) is based off of one's base Fortitude and thus has a negligible effect as one Levels up? The trouble is, an Eggshell Top functions because its magic syncs with its owner's natural energies, which would logically make it increase one's increasing Fortitude, albeit by the same degree each time. I'm not sure how to explain this discrepancy, but this is the solution I'd prefer. Once again, I am open to other ideas.