User blog comment:Ricoindigo/WORK IN PROGRESS : Mage update patch for Season 6/@comment-24385282-20160129231851/@comment-24785464-20160130125055

Hey there Jason :)

The passive she unlocks at level 6 is actually gives Miasma exactly what you're talking about, as the more health is missing and the more seconds have passed since the target is poisoned, the more it will be damaged. Truth in Venom could amplify this damage even further (and that may have to be toned down actually as it is a whole lot of damage amplification).

About the Miasma working on a stack system, it's an idea I had but it would need some shift in power in the rest of the kit as it might turn her into a zoning god... I mean, it is a good idea but stacking Miasmas on top of each other would contrast with the idea of clarity that Riot has nowadays.