Upon reaching Castle Ensis, the first boss in Elden Ring's Shadow of the Erdtree DLC, you encounter Rellana, Twin Moon Knight. Her attacks blend fast melee with powerful magic, making her an extremely challenging opponent. Here's how to prepare and defeat her.
General Tips 
•Preparation: Before facing Rellana, ensure you've upgraded your weapons and possibly leveled up or enhanced your Scadutree Blessing. This boss can be quite challenging.
•Summoning: Summoning allies can help manage her aggression. Use the NPC summon, Needle Knight Leda, from the gold marking on the ground, and consider using a strong Spirit Ash like Mimic Tear for additional support.
Phase 1 Strategy 
Attack Patterns:
•Glintblades: She conjures blades above her head which shoot towards her target after a delay. Use this delay to reposition or attack.
•Cross Slash: After some combos, she performs a cross slash with both blades, leaving her open momentarily.
•Magic Arc: She sends a spectral arc towards you, which you can dodge by rolling to the side.
Strategy:
Avoid panic rolling. Rellana's attacks are fluid, often changing mid-combo. Patience in dodging can create openings for attacks. Utilize light or medium weapons for quick attacks then retreat tactics due to her fast recovery.
Phase 2 Strategy
New Abilities:
Her swords now glow, one with fire and one with magic, enhancing her attacks.
•Fire Tornado: Starts with a fire storm around her, followed by pillars of flame. Watch for glowing spots to dodge the pillars.
•Moon Crash: Summons moons that crash down, creating shockwaves. Time your jumps and rolls to avoid these.
Strategy:
Keep your distance initially to observe her new attacks. Use her recovery from larger spells like the moon crash to get attacks in or heal. If you're using magic, spells like Glintstone Icecrag can exploit her vulnerability to frost, especially beneficial if you can stagger her.
General Combat Tips
•Dodging: Roll into or past her attacks, especially when she performs forward-facing moves. This can position you for counterattacks.
•Magic Users: If you have a magic build, spells that cause Frostbite are highly effective. However, note that she has high magic defense, so close-quarters magic might not be as effective without strategic positioning or the Terra Magica spell for damage boost.
•Melee Users: Fast weapons with good reach can maintain pressure without overcommitting. Remember, heavy jump attacks might allow you to stay safe as you recover under her swings.
Rewards
Upon defeating Rellana, you get the Remembrance of the Twin Moon Knight, which you can trade for one of two items:
•Rellana's Twin Blades: A dual-handed light greatsword needing 13 Strength, 16 Dexterity, 16 Intelligence, and 16 Faith. It has unique combo capabilities.
•A spell or another item relevant to your build.
Conclusion
Rellana is not just about brute force, but rather about understanding her rhythm, using the right moments to strike, and employing all your tools wisely, whether summoning, magic, or unique weaponry. In Elden Ring's challenging boss encounters, she teaches precision, timing, and how to make use of your environment and allies. Each move she makes is an opportunity.
