User blog comment:BerryBandit/Mechanically demanding champions/Quick decision champions/@comment-4952847-20130624194559

Someone below mentioned Anivia and I agree.

She's usually not what you'd think of as 'requiring quick thinking' since everything about her is kinda slow, but in teamfights, managing her stun and wall are some of the most difficult tasks (especially when your wall can make or break the fight in the correct position).

It's not that she requires you to be constantly thinking of the next step, it's that she requires you to be aware of what tools the enemies have and how you will react to those situations.

Her wall can the single most rewarding skill in the whole game if used right, but without quick and accurate judgement to back it, it can backfire just as easily.