No, its just not allowed to control another character, the two characters can have a conversation, and if I decide my character wants to go to the healer, then we can go. I'll give you some examples :)
Power Playing: (lets say I am Jane and the other person is John) Jane ran to John and began yelling then she hit John and pushed him in a river where he was swept away.
(I hit and pushed John without giving the other person a chance to make a move, so I controlled their character)
Regular Playing: (Me)Jane ran to John and started yelling, she aimed a punch for his stomach.
(Then the other person can respond and decide whether the punch lands or not)
(Other person) John dodged the punch but slipped and fell into the river.
If there is a fight scene or something else that player have agreed upon, for instance the people who play Jane and John decided there would be a fight and Jane would lose, then the rping would go something like this
(Me, Jane) Jane ran to up to John and tried to hit him, but failed, her punches falling on empty air.
(Other person, John) John succesfully dodged all of Jane's attacks and swung a fist towards her face, it landed with a smack.
(Me, Jane) Jane stumbled backwards from the hit and fell over.
I hope this helps clear things up! I know how confusing things can be at first... everyone gets confused so don't worry! :D:D
Clear with Temps dropping into the Teens
