|“||When a Blur spell is cast, the wizard causes the outline of his form to become blurred, shifting and wavering. This distortion causes all missile and melee attacks against the caster to be made with a -3 penalty. The wizard also gains a +1 bonus to all of his Saving Throws.||”|
This spell stacks with itself, and the "-3 penalty" is implemented as an armor class boost. It's not surprising Blur scrolls were not available until Chapter 6. Most (competent) enemy wizards will use this spell, and certain bosses have items that imparts its effects when a map is loaded.