This is how I would make that idea work:
Warlock's Diadem
- Unique Active: You take damage equal to 10% of your current health over 5 seconds, gaining Grievous Wounds and regaining an equal amount of dark mana* over that time. 5-second cooldown.
- Unique Passive - Thirst: Your non-dark mana regen is reduced by 65%.
- Unique Passive - Hunger: Spells you cast that use dark mana gain 15-30% spell vamp versus champions (scaling with your missing health), which ignores Grievous Wounds. This spell vamp is halved for area of effect abilities, and is also proportional to the percentage of the spell's mana cost paid with dark mana.
*(Dark mana is just like regular mana, but looks different in your mana bar and interacts with the passive components of this item. Dark mana is always used first)
This captures the idea of using your health for mana without having too strong of an interaction with healers. You gain Grievous Wounds while gaining mana and losing health with this item, making it difficult for healers to keep you up, but it also gives you the chance to earn that health back by casting spells with the mana granted by it. However, it lowers your natural mana regen, meaning you depend on this item for your mana.
The weaker you get, the weaker the mana sustain you get from it, but the more powerful the dark mana spell vamp gets, letting you get the health you need to cast your spells.
This is just the active/passive component. I could see it also giving a good chunk of AP, CDR, and/or health/health regen. This item would be great on mana-hungry casters that can afford to be a little low, or any AP champion that has good self-sustain, especially with shields instead of health.
And every champion that can heal
Now how can we make that any good ?
that's the problem for today