Mordecai's second argument against the ring: events that activate magic are a real danger.
Brought up as precedent while Mordecai is dismantling Carl's case for keeping the Night Wyrm's Ring. Does Carl not remember the magic pulses on the third floor? Events that activate magic are a real danger, and there will be traps that fire your own spells and items for you.
Triggering something like that while wearing a cursed artifact could be devastating — a point Carl has no answer to, and which does as much to get the ring off his hand as the threat about Princess Donut.
A third-floor event, now cited as a general warning about magic-triggering traps.