The weapon doesn't appear to be on my spawnlist.

Weapons should appear in the Fidget Spinner category. If they don't appear then you have an error, or the error is in your side.

you have autism

you have autism

When killing some NPCs (specifically in my case the Donkey Kong from Super Smash Bros. 64 Player Models + NPC's) with the shuriken version it crashes everyone's game who is connected to the server.

Since be a physics problem due to the NPCs you use. Our fidget spinners basically use the default physic & if it works for killing some players, it should work for killing every NPC which uses a proper physic.

The shuriken spinner does not damage anyone, but it used to.

Honestly I would say "yeah it's my fault" if I had an error or something which happens - but basically you are more or less the only one saying that it doesn't work, so it's probably in your side.
Are you trying to make damage by throwing a shuriken against a NPC, a player or what....
It just uses some physic logics with the speed of the shuriken and it should make a player is dying due to the high amount of damage you receive BUT if you change any physic parameter, it can make you don't receive any damage. Basically it can be due to the use of Prop Protection systems - I don't know how they are coded but a protection can disable the physic damage received between the ENT (shuriken) & a player. Only my opinion tho, normally everything should be good.