There are some questions out there about how to defeat Adil, Lord of the Fallen, so we've provided some strategies to help you out. If you need more information, check out our detailed guide.
In the ending of Adil, the lighthouse cannot be purified, and it is best to defeat the swamp boss, the hollow crow, and the tower of confession boss first.
After defeating these four, the castle is unlocked. To go to the castle, you must fight the monastery boss or huntress to obtain the Adil rune. It is best not to explore it first.
Enter the castle after killing the Iron Walker at the blessed gate of Karas. Kill the king along the way and talk to Adil. He will strengthen the runes and then go to the lighthouse to do ulterior things. The order of the lighthouses does not matter. After infecting the lighthouses on the upper level of the swamp, the cold land, the Tower of Penance, and Karas with Adil runes, go to the highest light sentinel, and then infest the last lighthouse.
I'm not sure if I have to talk to Adil again, but I did, and then interact with the panting woman in front of the Light Sentinel Lighthouse to complete the Adil ending, which comes with a set of clothes and unlocks the lord profession.