u/Sure_Fisherman_752

I've just checked. It gives additional Ability Haste to E and R, even if you don't build Rylai. They haven't implemented the extension of the effect yet as it shows stacks on enemy, which later should fall off one after another. Probably huge nerf to Nami due to lack of slow application, but Seraphine is among the few who can keep the debuff across the whole battle because double cast E applies this effect for 8 seconds (12 right after ultimate), but requires Rylai or Ashe.

Will check later in a real game.