Idea for Teemo's Shrooms in His Eventual Rework
Teemo needs some counter-play, but his core character focus (blind darts and poison shrooms) doesn't leave a lot of leeway for interesting gameplay. Riot Scruffy acknowledged it in his Q&A on Friday. There's a reason you (and others) despise Teemo, and it's because he's completely un-fun to play against because of these core focuses.
EDIT: I was incorrect about the blind dart applying poison damage. Rethinking how to fix his dart.
I think that with a buff to damage, the easiest way to add counterplay to Teemo's shrooms is to add a window of time in which one can skillfully dodge or mitigate damage from them. I was thinking a short startup time--short enough where pivoting backwards or using a mobility spell to dash would dodge it, but not long enough where one could literally just walk right over it and dodge it--where the mushroom bulges and explodes in a shower of poison could fix it.
Buff the damage a bit, or allow Teemo to place significantly more shrooms, but I think this would add an element to the (literally) toxic shrooms people hate.
UberAffe had this to add: "...if [shrooms] have delayed damage on activation they should also be active the moment he places them. This would keep the amount of time until a shroom can do damage about the same." I think this would go perfectly with my suggestion.
Sozan5's suggestion: "The other thing I could see working is that the mushroom is revealed and start exploding once you are close to it (just like in your idea), however if you do get into the 60-range (the normal exploding range of the mushroom) it will explode immidiately - so you cannot just run or jump through the mushroom - you have to either retreat a bit or at least go sideways. This will still contribute to mobility creep but only a little bit (since you wouldn't be able to just dash through the shroom)."
Posted this on Reddit but thought it'd get more traction here.