Crysknives don’t revert if you’ve killed a monster with it since the last time you picked it up.

When a crysknife leaves your inventory, it starts a timer with 10-50 turns. The timer is canceled if it reenters your inventory. If the timer times out on an unfixed crysknife, it reverts to a worm tooth; if a fixed one times out, it loses one point of enchantment and restarts the timer, or if it’s at +0 it reverts to a worm tooth.

Trying to enchant multiple crysknives at once will fuse them together before trying the enchantment.

If you enchant multiple worm teeth into a single crysknife, the enchantment of the resulting knife is increased by 1 point for each additional tooth involved. This can go up to a maximum of +9, bypassing normal overenchantment dangers.

Fixed crysknives never revert.