Rellana, Twin Moon Knight is a boss in Elden Ring Shadow of the Erdtree, waiting for you at the end of Castle Ensis. Rellana is one of the deadliest knights in a game full of them, using two swords infused with fire and magic to unleash heavy combos on players and tear through their defences, but unfortunately there's no way to avoid her: sooner or later, if you want to progress through Shadow of the Erdtree, you'll have to beat this mandatory boss.
So considering that she's one of the Shadow of the Erdtree main bosses, there's a few things to cover first. For one thing, I definitely recommend you get all the Scadutree Fragments in Shadow of the Erdtree available to you so far, as you'll need the power boost. Secondly, if you haven't beaten the Divine Beast Dancing Lion yet, I recommend taking on that first, as it's the easier of the two encounters, and worth doing before you progress on to Scadu Altus.
