Fizz's spells scale off Ability Power - consider getting items like Zhonya's Hourglass or Banshee's Veil against teams that have high burst threat - and items like Lich Bane or Rabadon's Deathcap if you think you can survive without the Health.
Since Fizz can move through units, find opportunities in lane to walk through minions and apply Seastone Trident's passive - following it up with the ability's active attack after a few seconds.
Fizz's ultimate ability, Chum the Waters, can be aimed at an enemy or towards the area where you think they'll be going.
Lay Waste is very strong at farming minions and harassing enemy champions.
Ask your allies to help point out when you should use Requiem to get kills in different lanes.
The Fizz Karthus synergy stats shown here demonstrate the areas of his gameplay that do better (or worse) when paired with Karthus, compared to his overall stats. Significant differences are areas of focus that highlight how his gameplay changes when paired with this other champion.
Overall, Fizz sees a large worsening in his KDA (ratio of kills and assists to deaths) when paired with Karthus. His KDA worsened from NaN to NaN. This worsening shows that Karthus helps Fizz perform worse in ranked League rounds. Yet, the small difference shows that this performance change is not very impactful.
When Fizz plays on the same team as Karthus, he observes a little increase in his total damage output. This difference could demonstrate that Karthus provides protection for him to dish out more damage or that his support also helps extend the game's duration. Similarly, when Fizz is played alongside Karthus on the same side, he usually scores many fewer killing sprees than when he plays without Karthus. This is contrasting evidence that he is worse when playing synergisticly with Karthus.
Moreover, when Fizz plays with Karthus on the same team, he usually takes more damage than when he fights alone. Getting dealt more damage could indicate that Karthus does a poor job of protecting Fizz in team fights.
There is no universally accepted best synergy for Fizz that will always be his top ally. Yet, Karthus is a below average teammate for Fizz. By being on the same team as Fizz, he decreases their win rate by -1.3% to 51.3%. This clearly indicates that there is a bad strategic relationship between Fizz and Karthus that results in them performing not as well together than alone.
Karthus has a greater difficulty than Fizz. That means Fizz players need to be cautious when lining up Karthus comrades to go into battle on the same side as, as they will have to have a greater level of skill to play well with you.
Working cooperatively, you will likely witness an overall large increase in your team’s ability to deal magic damage. Combined, these champs can blast through enemies with magic damage.
Conversely, by pairing Fizz and Karthus together, you may not be granting your other teammates very much support. Make sure to pick other champions on your team that fills this relative gap in this pairing's capabilities.
Regardless of the skill of your Karthus ally, you should focus on maximizing your income, staying alive by avoiding foolish fights, and clearing objectives. If you do this, you should do well anyway.
If you would like to truly master Fizz to synergize with Karthus during both the early game and mid / late game phases of League rounds, you should keep reading to master a few extra lessons on this champion pairing. If you listen to the build and suggestions presented above, you will grow your win rate significantly.
The most important items to have in your Fizz and Karthus synergy build consist of Void Staff, Zhonya's Hourglass, and Stormsurge. When Fizz combined at least these three pieces in his build, he did much better as an ally of Karthus than with most other common item sets. In fact, Fizz had an average win rate of 51.3% when synergizing his build and playstyle to Karthus with these items in his kit.
To have the greatest probability of crushing your oponents, you should use the Electrocute, Sudden Impact, Eyeball Collection, Treasure Hunter, Triumph, and Coup de Grace runes from the Domination and Precision rune sets. Out of all the rune builds we have analyed for this team composition, this composite of runes yielded the best win rate. In fact, these runes averaged a 51.3% winrate overall.
If you would like to get Fizz with Karthus synergy tips and builds for a an individual player tier, please choose one from the selection menu shown above. By default, the statistics and guides given are calculated using all games played with both champions.