There is a lot of incorrect info about this staff, let me clarify.
Elemental Staves: -2 Avatar & Elemental Perp (To corresponding element)
HQ Elemental Staves: -3 Avatar & Elemental Perp (To corresponding element)
Bahamut's Staff: -3 Avatar Perp (YES IT effects Elemental Spirits.)
and SMN skill (post update) now effects avatar accuracy (both BP and melee)