I did some math to find out which AP items were the best if you wanted as much damage as possible. I only did the math for Void staff, Horizon Focus, Shadowflame and Rabadon (considering you already have Luden and sorcerer boots).
In the end Horizon Focus is always higher if you can proc its effect. So I’m wondering why every Lux player for example aren’t buying it second item.
Wait this is just wrong though, unless you also do true/physical dmg shadowflame does more dmg until enemies have 120 MR
The benefit of building horizon is the 15 haste