General

@FallenLink thank you that was helpful

You forgot the Troll Scroll.

Shield Scrolls protects an item from losing a slot or something. Guardian protects the Scroll from disappearing if it fails. Return Scrolls allows you to keep the original stat of an item. Return scrolls help you return to town.

Reading comprehension 101.
Shield scroll = Protects your slot on the item you apply it on, that is if a scroll were to fail, the slot would not be consumed.
Guardian Scroll = Protects and returns the scroll to your inventory on the applied item IF the scroll fails. Usually used for expensive scrolls such as Unique 60%'s or AEE's.
Return Scroll = If you use a scroll, say a Chaos 60%, the return scroll lets you choose whether to apply the changes or not. Example, if a chaos scroll gives 0 attack, you'll use the return scroll to not apply that change because no one wants 0 attack. Also return scrolls help you return to town :V