Been trying a Dot zombie karthus build

Its just for fun and it works pretty well against non tanky comps even in the late game

Not really sure what items i should keep swap out. NO this is not for ranked chill out. What should i swap tho? I kinda want this to work its honestly really fun once it gets going and works pretty well.

Core:

Swap ins: (not sure what works best together yet) have to go together obviously or Try it in normals its pretty awesome. People really don't expect the damage. Use normal karthus runes tho.