Last Whisper + Void Staff = New Item
Cost: 2295 + 2290 + 515 = 4600

80 AP, 50 AD
Unique Passive: 40% ArP, 40% MPen

Picture based on Item name: Maybe a rod of some sort.

This is too expensive, and probably too broken actually, but maybe not. But hybrids need a single item that gives defense penetration (both). It makes hybridization more viable on more champs.

Too strong and too expensive.

One of the mods suggested something similar, but they suggested 20-25% of each and not build from LW and VS but it's still a good idea. That specific idea is OP, but the idea of hybrid pen isn't.