Nothing. They'll just send a letter back to you. An OK one. If you send them a mean one, they aren't very smart a reading letters so, they won't be mean to you unless Katrina tells a fortune that they will.
When you talk to the animal that gave you the letter, he/she will be mad at you.
Nothing. Depending if you wrote in chat speak or used proper grammar, the neighbor will reply saying that either you need to learn how to write or some random stuff, respectively.
you get a letter from mom. Inside of it, there are pink carnations
No. But on city folk you can list a complaint about one of your neighbor's
You cannot send a letter to the mayor on Animal Crossing City Folk. You can only send letters to neighbors and friends. The mayor is one of those 'non-neighbors' that are in your town, but you can't talk to them or send letters to them like a real neighbor.
You can't
If you open a gift or letter on Animal Crossing Wild World the person you were supposed to deliver it for will be very angry.
you can't
It is impossible to send a letter to any of the shops/buildings in the town and/or city in Animal Crossing City Folk. Letters can only be sent to other town folk.
no you cant 9 (sadley)
yes
Go to Tom Nook's Store, they come in a pack of 4.