The spell Astral Projection has a drawback listed:
While you are on the Astral Plane, your astral body is connected at all times to your physical body by a silvery cord. If the cord is broken, you are killed, astrally and physically. Luckily, very few things can destroy a silver cord. When a second body is formed on a different plane, the incorporeal silvery cord remains invisibly attached to the new body. If the second body or the astral form is slain, the cord simply returns to your body where it rests on the Material Plane, thereby reviving it from its state of suspended animation. Although astral projections are able to function on the Astral Plane, their actions affect only creatures existing on the Astral Plane; a physical body must be materialized on other planes.
This mentions that "very few" things can sever a silver cord, but not which things those are.
The one that I know of is a Githyanki silver sword. Is this the only effect in the game that explicitly allows the severing of silver cords? Are there rules anywhere that would allow a player or DM to determine whether a given attack is capable of affecting silver cords?
Best Answer
Manual of the Planes (p49) says
Planar Handbook: A Player's Guide the the Planes only mentions the ability of a psychic storm to damage a silver cord (p165), and The Eye of Gu’n’ragh magical location's (p174-5) recharge condition mentions damage to the cord for an astral traveler on a failed save.
So anything mentioning the silver cord specifically can damage or sever it, but anything not mentioned cannot. Wish or miracle might do it, but that's in the part of the spells requiring DM fiat.