There should be a way to tell what the acquired resistances of a monster are. This could be by zapping a wand of probing at it, by breaking a potion of enlightenment on it, feedback gained from a stethoscope, or (less likely) a new spell exclusively for pet diagnostics.

Note that it may not be considered “fair” for any of these methods to work on pets, but not work to tell the player’s resistances when they do it to themselves.

Any item can be dipped into a potion of levitation to permanently reduce its weight by 20%. This uses up the potion, and it will only affect the item’s base weight, not the weight of any contents (i.e. a bag of holding thus dipped will weigh 12 + contents instead of 15 + contents). If the object is canceled at a later point, it loses this property and reverts to its normal weight.

The effect cannot be stacked; attempting to dip an already-levitated object into another levitation potion will have no effect and will not use up the potion.

A possible variation is to also confer this effect for potions of enlightenment, since “enlightening” the item could be interpreted as making it physically lighter.

A cursed potion of enlightenment grants you temporary darkvision.

Monks start with potions or a wand of enlightenment.