Elden Ring: Shadow of the Erdtree is pretty rough, and that's mostly down to the game's first handful of hours. You can gradually get used to the difficulty as the DLC progresses, but some of the early boss fights can put you in your place for a substantial amount of time. Rellana, Twin Moon Knight is one such wall, a fast and brutal boss who can easily put you in your place if you underestimate her. She did me, anyway.
Thankfully, it seems as though there's a very easy way to cheese your way through the fight, and it doesn't require you to step foot into her arena at all. First shared by the Twitter account ZioStorm1, this strategy involves making your way to the back of Castle Ensis and running up to the fog wall that's to the rear of Rellana's arena.
Once there, you can press yourself up against the fog wall and cast the incantation Flame of the Fell God, which casts a slow-moving ball of fire that explodes on contact. Line yourself up against the fog wall properly, and this ball of fire will be cast inside the arena and slowly float towards Rellana, eventually...