Slowing attack

The Slowing attack, known as AD_SLOW in the source, is an attack possessed by some creatures, including shades and skeletons, which removes intrinsic speed, if you have it:

The shade touches you! The shade touches you! You slow down.

Slowing is successful only 1 in 4 times the attack hits, and is additionally affected by magic cancellation.

The (as yet unimplemented) beholder has source code for a slowing attack from its gaze. This appears to be unaffected by magic cancellation.