[Custom Item] Mithral Hand

[harmor]

Mithral Hand

Provides a -5 penalty to swim checks.
Provides a -2 penalty on concentration checks.
Natural Attack at -5: Deals damage as a monks unarmed strike of our character level.
Shocking Grasp (Su): deals 2d4 damage +1 point/level; useable once/2 character levels.
Immune to rusting grasp or the attacks of a rust monster, as a gauntlet of rust

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I pretty much can figure out the skill modifiers (copied the eval code from the Vest of Escape, but replace the skills), but the other stuff I'm not sure how to implement.

Any help would be appreciated.