A suggestion would be for you to find something similar to the item you're trying to use and check that it works, in this case try checking Rune sword/Rune Spear or the dragon equivalent, The animations set are probably incorrect for the anger sword/spear therefore make you invisible
- Find the item ID of a Rune Spear
- Open Weapondefinitions.xml
- Search rune spear ID
- Copy all code and paste it, change rune spear ID to anger spear and see how it goes.