Eureka

Per level³

• Eureka is recommended in a heavy ability power and ability haste build on Hwei, alongside ADAPt, Jeweled Gauntlet or Phenomenal Evil.⁴
• For an Autocast build, take one ability haste augment if possible; Eureka is one option alongside Accelerating Sorcery or Dark Blessing.⁵

Eureka can give Veigar enough ability haste for his Arena to have no cooldown.⁶

Casting Vladimir's E before W activates a flag that keeps E available throughout W, allowing another cast. With enough ability haste, he can cast E more than once during W; Eureka with Goliath is one example of how to reach that amount.⁷

• For an Autocast build, pair an ability haste augment such as Eureka with Hexbolt, Runecarver, Lightning Rod and level 3 Quantum Computing; Chromaflux, Wildfire, Self Destruct and Slime Time are suggested Autocasts.⁵

Earlier formats

Eureka can convert ability power granted through Talisman Donor into haste.⁸ 8x2 duos

With Eureka, one Maokai's ability power shared with another through Restart also gave the other ability haste.⁹ 8x2 duos

• A full mage build with Jeweled Gauntlet and Eureka is an option for Kayle.¹⁰ 8x2 duos
• Tahm Kench can take Eureka if Goliath, Wooglet's Witchcap or Blade Waltz is unavailable.¹¹ 8x2 duos
• Eureka was taken alongside Nesting Doll.¹² 8x2 duos
• A synergy between Slow and Steady, ADAPt, Eureka and Master of Duality let Ezreal gain ability power from attack damage and then convert that into ability haste, while Master of Duality stacked.¹³ 8x2 duos
• Eureka was part of a build with Gamba Anvil, Dashing and Hybrid; the build had short ability cooldowns.¹⁴ 8x2 duos