Since we're looking for a poison mage, why not Zyra?

To me, it fits with her intended sustained damage play style. She has a slow, snare and knockup. I think these tools lend themselves to someone with damage over time who has reason to lock the enemy up back to back to back.

Readjusting her damage/ratio numbers would probably be easier than trying to fix plant AI. I'm thinking that at least with the poison mage route, her plants just need to hit enemies once to be effective, and so for those times when they randomly switch targets, it wouldn't be that big of an issue (but they should still try and fix that)

I was watching Jumanji today and the part where the plants shoots out the sleeping dart gave me the idea.