Read about SR/IR vs. SRR/IRR. SR Revised V1.3.900: GitHub page, latest repository master. Click the "Code" button in the top right, then "Download ZIP" in the the dropdown menu. To install this, you must extract the latest official version of SR V4 (b18 or anything later should be fine!) to your game directory as you would normally (or have an automated tool do it for you), and then additionally extract this mod on top of it before installing SR. Specifically, SRR's spell_rev folder should