Corrosion (Japanese: ), abbreviated Corrsion, is a skill used by Seth in Phantasy Star IV: The End of the Millennium. It deals physical damage to all enemies equal to 144 plus Seth's mental stat, modified by each enemy's physical sensitivity and defense stat. Some monsters, including Slugs, Scorpions and Zombies are resistant to physical damage; Ghosts, Dimensional Demons, and some bosses are immune to physical damage. Some creatures, such as Haunts and Chaos Sorcerers, can use this spell.
Seth already knows Corrosion when he joins the party.