Witch themed champion

Passive: field of misery Gains a charge of misery each time she kills an enemy minion. Gains 1 AP for each misery charge, up to a maximum of 100.

Q - Curse of pestilence When the next enemy minion nearby dies, it gives 3 extra misery stacks and restores X health and Y mana. The corpse then creates one small herald of pestilence that applies Z damage over time to units around it. (Note X and Y are small, but mana cost shouldn't be outweighed by the return, so likely no scaling on it. Health however, might)

W - Rot Target area becomes a swamp for X seconds, slowing movement speed for Y seconds of all units within it. Reactivate within the duration to use 5 misery stacks to stun all units standing on the swamp and dealing Y damage.

E - Curse of Ruin When cast on a unit, it removes X armor and magic resist, dealing Y damage over time. Reactivate to use 10 misery stacks to silence and blind the target for 1.5/1.75/2/2.25/2.5 seconds. When cast on a turret, deals Z damage and degrades the turrets damage for a period of time. Gain 1 misery stack per second while active on a turret, duration scaling based on total number of stacks. Reactivate on a turret to use every misery stack generated during thr spell plus 5 to deal V damage to the turret (based on stacks used)

R - voodoo Target enemy champion takes increased magical damage and deals damage in an AoE based on how much damage the target has taken and its max health. Reactivate to consume all stacks of misery and deal damage based on how many were consumed. If the enemy dies during the ults duration, you get W AP permanently and half the stacks used are refunded.

Bit of a feast or famine lane bully. No mobility, but moderate lockdown and (I hope) a thematic kit.