Anti-magic fields in Gehennom can attempt to cancel you or your gear, and apply the cancelled status effect.

Scale the damage from an anti-magic field (caused by having MR so you don’t get drained of magic power) to your maximum HP, or possibly by your experience level, rather than a few d4s that are usually meaningless to any character with a few levels. Or have it be based on your Pw maximum, with a higher maximum incurring a larger amount of HP damage.

Triggering an anti-magic field, in addition to draining some of your energy, removes any magical buffs or debuffs applied to you, similar to how cancellation works as described in #2673.

The player can’t cast spells or use magic items while standing on top of an anti-magic field. (Rather than straight up not being able to use the magic items, they would behave either like their non-magic counterparts, or as if they had no charges, as much as possible. Magic instruments would play normally, wands would fail to produce an effect, scrolls would have no effect, and so on.)

Anti-magic fields end a bunch of temporary magical intrinsics, such as speed or see invisible.