Illos is studying the cause of the forest contamination, and he said that he needed an Arachna’s Poison Sac for his research. Gather one and bring it to Illos.
Step 1. Bring a Tiny ArachnaAn arthropod found all along the road from the Contaminated Forest to the Altar of the Crimson Dragon.‘s Poison Sac to Illos. (You need to collect: Arachna Poison Sac)