For the glitch you will need: -100 Sneaking -1 Daedric arrow (Explained in post) -Invisibility potion -Spare time (Depending on amount of arrows wanted) -Common sense Okay so you get the arrow what you are wanting to duplicate in your inv. I would recommend either Ebony or Daedric because they are the best arrows on the game and are quite hard to find. To get a Daedric arrow go to the Fletcher in solitude and he should have 1. If not be patient and wait for a few days and come back, if your lucky he should have a single Daedric arrow for you. (This took me 6 days of waiting.) Then go to the guards that are training archery outside Castle Dour, Crack a invisibility potion open, Steal the arrows what the guard is shooting and replace them with the single Daedric arrow that you have bought from the fletcher. Then he should continuously shoot Daedric Arrows from 8am-8pm then he will go to sleep. You can get hundreds of arrows from this method! (Its the easiest/quickest/cheapest and best way to get arrows on Skyrim.)
