Burn the first and second giant webs
Use E. Gadd’s key on the Lobby elevator and descend to the Cellar. Pull the web to start the battle. When the spider opens its eyes, stun it with the Strobulb. Grab the central web ball and back away until the torch-bearing armor lowers its flame onto the web. When the spider falls, stun and vacuum the Grouchy Possessor, charging a full Power Surge to break its protection.
After it returns to the spider, dodge the charge. Spin the hanging fan so its web ball catches fire and clears the side webs. This exposes a spear-bearing armor. Stun the spider again and drag its central web ball onto that spear, then spin the burning hanging ball into the attached web to ignite the large barrier.
Expose the final torch and capture the Possessor
Vacuum the Possessor again after the second fall. In the last spider phase, take the loose web ball on the right to the first torch and ignite it. Carry it back to burn the web hiding the armor on the left. Its torch lights once uncovered. Stun the spider, pull the central web ball toward this newly exposed flame and burn the last giant web. Capture the Possessor after its third exposure and collect the Dark Moon piece. If a pull is interrupted, reposition and stun the spider again rather than forcing the web through its attack.