Item concept: Blood Goblet
Description: Ap/health version of Muramana and maw of Malmortius.
Rough example:
Crystalline Bracer + Needlessly large rod + Ruby Crystal = Blood Goblet(3200g~) -80 ap -300 health -100% base health regen
Passive 1: Grants 1.5 ability power for every 2.5% of missing health, up to a maximum of 45 ability power.
Passive 2, Toggle: Single target Spells and attacks consume 3% of current health to deal bonus magical damage equal to twice the amount of health consumed.
p.s. as i was creating this post It occurred to me that there could possibly be a health version of tear of the goddess that stacked health somehow, which would of course build into Blood Goblet.
If the stats and scaling are too strong it can be toned down for balance.