Fiend-Shen’s room alternates between water, ice and a fiery setting. The inspected fights use the Fairy Slinger toward the marked tail end while body segments remain. Treat the current terrain and the marked target as separate things to track.
Identify the equipment and target
The blue two-lobed item used in the fight is labelled Fairy Slinger in the developer’s equipment menu in another recording. Equipment label
At the start of the fight, a pink-and-green marker appears beyond the spiked body segments. In both recordings, the player faces toward that end and sends the fairy along the line of the shot. The independently recorded sequence at 7:06–7:16 shows the target moving around the arena as the segmented body follows the perimeter. Independent tail sequence · Developer sequence
Reposition when the room changes
The small central island is used during the water phase in both videos. When the room changes, recheck the floor and the boss’s position before continuing to fire. The fiery version can contain lines of flame, while the ice version removes the visual water channels. Terrain changes
Do not assume the centre is permanently safe. These are observed positions in successful fights, not an invulnerable spot.
When only the head remains
When the long chain disappears, keep tracking the small detached tail target rather than aiming only at the large head. The independent video shows the marker on that small target at 7:29 and another Fairy Slinger shot toward it at 7:31, followed by the head’s damage effect. The developer’s 17:05–17:11 sequence shows the same detached target and marked shots. Continue that targeting pattern while avoiding the head and its projectiles. Independent late phase · Developer late phase
A heart reward appears after the defeat. For a fully documented fight using the Fairy Slinger with another tool, see the Arbiter; that page contains final-boss spoilers.
Sources: developer and community fight recordings. This covers the boss encounter, not the route through Wyrm’s Remains.