First of all, deal with the corruption that hangs around in the first room. Then use the blue flame at the entrance to light a torch and locate yourself in the semi-darkness and unblock the first entrance by igniting the pedestal next to it. Same operation in the second: elimination of corruption and opening the next door with the blue flame. You should then arrive at the checkpoint and open Rudania's roof. From now on, it will be possible to tilt the entire dungeon by 90°.
Terminal 1
Terminal 2
Terminal 3
Terminal 4
Terminal 5
Boss
Now that all terminals are on, go back to Rutania's back to begin the fight against the dungeon boss. The fire shadow has two phases: in the first phase, it will throw lots of small fireballs and give big sword blows. Stay away and aim at its eye to make it fall. Use the spear to reach it if it remains suspended in the air. In the middle of its life, it will get angry and prepare huge flaming projectiles: drop a bomb at the moment it casts its attack, then run and hit it as many times as possible as soon as it falls.
Written by Bastien "Lloyd" Dubosq-Luyer. Translated from French by Millenium.us.org.