What If There Was A Champion Who ACTUALLY Poisoned Enemies?

Disclaimer; I have NO IDEA how RIOT would be able to make either of these a balanced, neither under-powered nor overpowered champion, but the basic Idea is as follows; Instead of a short DOT effect like most poison wielders, the champion would inflict a semi-permanent, or at least long duration debuff when "poisoning" enemies. it would start fairly weak, some might say unnoticeable, (that's part of what makes poison so intimidating after all, you can die before you even realize it's in your system) but the more they re-apply the effect, the worse it gets. You might survive the first engagement, walk away taking less than 1 hp damage per 5 seconds, but until you die (or for several minutes, either or would work), it sticks around. Next engagement, you got pegged with the poison-delivering attack again, maybe now you notice, but it's still not terrible. Third time around, now you have a problem, your champion feels sick, and their health bar shows it, you power through, but the poisoner gets you again, your champion's in serious pain, your hp just isn't sticking around.

Alternatively the debuff could reduce a character's maximum hp value, or defense values cumulatively until they manage to wait out the debuff duration/die if it's a semi-permanent debuff.

Again, NO IDEA how RIOT would balance it, but it'd be pretty cool to see some poison that acts, well... Less like being hit with ignite, and more like the real McCoy.