Use Fizz's high early game agency to invade and disrupt Karthus's full clears before he scales into his global damage power spike.
Focus on controlling river vision and contesting Scuttle Crabs when your lanes have priority to secure safer objective setups and deny Karthus tempo.
Jungle Plan
Invade Karthus early to force him off camps and reset his tempo, leveraging your stronger level 3 dueling power.
Prioritize river vision control and contest Scuttle when lanes have priority to secure objectives safely.
Counter-jungle opposite side camps when Karthus is visible or after forcing him off his jungle to deny farm and scaling.
Danger windows
Avoid invading during Karthus's first full clear reset timing when he can respond quickly or has lane priority to collapse.
Isolated river fights without vision are risky due to (Q) and (E) damage punishing low-health clears.
Objective setups become dangerous after Karthus reaches level 6 with (R); avoid extended fights without vision and lane support.
Early game
Start with a three-camp clear to hit level 3 quickly and look for early invades on Karthus before he completes his first full clear.
Contest first Scuttle only if nearby lanes have priority to support fights or counter-ganks.
Avoid extended river fights without vision, as (Q) and (E) damage punish low-health isolated clears.
Power spikes
Level 3 unlocks your full engage combo with (Q), (W), and (E), enabling strong dueling and invade potential; use this to pressure Karthus's jungle.
Level 6 (R) grants a powerful all-in tool to secure kills or force Karthus out of objectives; track this cooldown for aggressive plays.
Completing your first AP assassin item increases burst damage, allowing you to punish Karthus's weaker early fights and contest objectives more confidently.
Win conditions
Convert early invade success and level 3 power spikes into denying Karthus's camps and forcing him behind on tempo.
Use superior mobility and gank threat to pressure lanes, secure Scuttle Crabs, and set up early dragons or Rift Herald.
Maintain river control and vision to force Karthus into unfavorable fights and prevent him from scaling into his global damage windows.
Tip: For Fizz vs Karthus, read overview, trading pattern, and danger windows first for a fast Jungle lane check.
