How to rebalance Teemo?
As he is now, Teemo can never be allowed to be actively powerful due to his lack of counter-play. We should help Riot come up with some ways to make him powerful, but include things that people can do to fight back against a 25 kill Teemo.
I think a good mindset would be to have him as an AP assassin, rather than a AP marskman.
Old:
Camouflage - If Teemo stands still and takes no action for 2 seconds, he becomes stealthed. Taking any action or being moved will break his camouflage, giving Teemo the Element of Surprise, 40% bonus attack speed for 3 seconds.
Blinding Dart - Active: Teemo shoots a dart at an enemy, dealing magic damage and blinding them for a few seconds.
Move Quick - Passive: Teemo gains increased movement speed. Damage from champions and structures will disable this bonus for 5 seconds. Active: For 3 seconds, Teemo doubles his passive movement speed bonus. While active, Move Quick's bonus cannot be disabled via champion or structure damage.
Toxic Shot - Passive: Teemo's auto-attacks deal bonus magic damage and poison his target, causing them to take additional magic damage over 4 seconds. Subsequent attacks only refresh the duration.
Noxious Trap - Active: Teemo places a mushroom trap on the ground for 10 minute, which stealths and arms after 1 second. While armed, the traps grant vision in a 212.5-radius. If an enemy comes within 60-range of the trap, it will detonate, slowing and dealing magic damage over 4 seconds to nearby enemies within 200-radius.
New:
Camouflage - If Teemo stands still and takes no action for 2 seconds, he becomes stealthed. Taking any action or being moved will break his camouflage, giving Teemo the Element of Surprise for 3 seconds. Teemo's next basic attack or Blinding Dart will deal an additional 20~140(+0.5) AP damage.
This is one of the changes that will help to emphasize his "Hit and run" style of gameplay, while lowering the power of "Blind them then auto to death."
Blinding Dart - Active: Teemo shoots a dart at an enemy, dealing magic damage and reducing their vision to 500/475/450/425/400 for a few seconds.
No one likes standing right next to Teemo and being unable to hit him while he spams his laugh. Reducing vision instead allows people to fight back if he doesn't properly space, while still keeping it as a powerful tool against long ranged foes.
Move Quick - Passive: Teemo gains increased movement speed. Damage from champions and structures will disable this bonus for 5 seconds. Active: Teemo breaks free of all slows and for 3 seconds he has double his passive movement speed bonus. While active, Move Quick's bonus cannot be disabled via champion or structure damage.
I think that his Move Quick is pretty great as it. It allows him to quickly roam the map and get into position. Breaking free of slows allows to to better reflect his new "get in then get out" assassin play style though.
Toxic Shot - Passive: Teemo's auto-attacks deal bonus magic damage and poison his target, causing them to take additional magic damage over 5(!) seconds. Subsequent attacks only refresh the duration. Total Magic Damage Over Time: 50 / 80 / 110 / 140 / 170 (+100% AP)
By removing the stronger on hit portion and giving it a longer duration Teemo is encouraged to be slippery and "spread the love" in team fights to maximize his power. The low base and high ratio is to keep him in control during the lane phase if he maxes his E first.
Noxious Trap - Active: Teemo generates a new trap periodically, and can only store up to 3 traps at once.
Active: Teemo places a mushroom trap on the ground for 10 minute, which stealths and arms after 1 second. While armed, the traps grant vision in a 50 radius. If an enemy comes within 50 range of the trap, it will detonate after half a second, revealing nearby enemies within a 250 radius for (5/6/7) seconds and inflicting a decaying slow of 30/40/50% (+5% per 100 AP).
This skill will never be allowed to both deal damage AND be good. I instead suggest that it be made into a utility ult, allowing Teemo to locate and track his prey, the powerful slow preventing their escape until he arrives.