Your Grandmother took away your Wii because you did not adhere to the rules and guidelines she set for you. By asking for help on how to get it back, you're effectively tricking your Grandmother into giving it back to you, because the actions that you're going to do aren't sincere. They aren't for helping her, or doing something nice to her, it's to get back what she took away from you.
If you want my advice, here it is. Take the punishment, and wait for her to give it back to you naturally. No fake chores, no fake gifts. Ask her when she'll give it back to you, and wait. She's eventually going to notice that you have learned your lesson, and give it back. If you go the other way, it's going to be painfully obvious to her that you want it back, since you started doing nice things to her in succession after it got taken away. That will only lead to her to keeping it longer.
You may think your Grandmother hates you for taking your Wii away, but she's actually giving you tough love. She knows better than you. She knows the hazards that come with not getting the full 8-hour sleep, she knows how bad it is to play in the dark and etc. You may not understand it now, but trust me, you'll understand it when you're older.
Even I get punished, and I'm already 20 years old. Parents/guardians are forgiving and understanding. It usually goes like this: If it's their roof, and they feed you, it's their rules you have to follow. Unless you provide your own money for food/rent/necessities and whatever you need, you have to follow them. It's the least you can do for them giving you a roof over your head. I know this sounds preachy and very mom-like, but it's the truth. This is how the world works. Give and take. There is no take, take, take. Equivalent exchange.
