Why
Lee Sin disrupts Amumu's default plan from jungle tempo: they can deny your key kit windows. The matchup is mostly decided by trade pattern, and one bad window can flip control immediately.
Lane impact
You can lose jungle priority: fewer dragons, less vision, and forced ganks on bad timings. This matchup is mostly expressed through pathing reads, scuttle priority, and who reaches neutral objectives first. If you miss one tempo cycle, you lose priority and hand over roam or objective timing.
How to play
Path safely, ward entrances, avoid early 1v1s, and look for plays on lanes with CC to guarantee Bandage hits. Adjust positioning before each trade and adapt pathing/rotation to wave state. Key timing: level 5 and first neutral objective; concrete decision: if window is closed, cross-map or tempo reset, otherwise commit only after confirmed enemy cooldown usage.