Horizon of Darkness

It won't have 4 levels because that would be too overpowered. It works by reserving one skill slot and one VI-level charge permanently. This means you'll have fewer charges at that level. There's no need to pass a check; it's a passive, unremovable skill. And it's a bonus to all experience gained; the character will receive 15% more experience. Even with a demon, it's unremovable, but I can provide information about 2 demons...