The Worm's Back
Key Strategy
Use the moving body segments as temporary platforms and focus your attacks on the exposed weak point along the top. Short jump attacks are safer than long grounded combos because the arena is constantly moving.
If poison buildup is the main reason your attempts are failing, prioritize movement and positioning instead of forcing damage.
Common Mistake
Do not stay on one segment for too long. Reposition early, watch the next safe landing point, and attack only when the weak point is clearly reachable.