Voidform

Void Eruption tears reality open — each stack increases all damage you deal by 3% (compounding) and your attack speed by 2%, up to 10 stacks. Your shadow damage-over-time ticks add stacks and hold the rift wider; it collapses 10 seconds after your rot stops ticking.

Nothing in the game currently grants this. It may be unused content, or reachable only through a system this wiki cannot see.