They ' ve implemented replays at PBE server exclusive for open beta testing in 2013 . The problem they ' ve pointed at that time is the same we still have compatibility with previous patches . As someone with no experience in game design aside some Unity beginner projects , but who has experience working as a programmer in a 500 employees environment , I think the data in League of Legends is organized in a way they can ' t develop a proper replay system or sandboxpractice mode without ditching the actual engine and developing a brand new engine , and the project managers or any similar shit there don ' t see the need to spent all the time needed to do that in features that , in their vision , won ' t bring ROI to Riot . I ' ve heard somewhere that champion skins are programmed as different champions hence why some bugs are observable only in specific skins of a champion . And considering some PR statements from some people at Riot , I imagine they ' re oblivious or plain stupid enough to think a proper replay system or sandbox aren ' t needed . TLDR Riot Games fucked up the entire thing somewhere in the development of the game and they ' re stuck on that situation because of the mentality of the big guys there .