A death ray zapped over a monster egg on the floor kills it, making it so that it will never hatch.

Possibly, this effect could also be achieved by erodeproofing or canceling the egg.

A Wand of Orcus artifact, no longer an actual wand of death but now a quarterstaff or mace. It can be invoked to shoot death rays (perhaps with some limitations to avoid overpowering it). Orcus can use it to shoot a death ray at will, without any sort of invoke cooldown.

All angelic creatures should be immune to death rays.