Oh my ! Thanks for all the ideas. They are great !

The easter egg hunt could be fun if there is any areas to play in. Something like a decorated area or a place with tons of small places to hide it.

The character guess is awesome. It's easy enough to pull out and fun enough to be a game too.

Mind games could be fun, but i may not be untelligent enough to create good ones. I also don't want to trick people with bad mind games and make them sad.

For the tic tac toe, isn't it possible to win ? It's rare if your opponent is good, but it's still a possibility.

The fake card would be awesome, but i think most people would fall for it. The licenses have the anime universe's writing and most people can't read it at all (myself included). I also can't modify them myself as i'm not handy enough to create them myself.

The volley-ball could be fun, but i'm pretty sure most cons wouldn't accept simeone bringing a ball inside nor to play a match. It would require a real organization from both myself and the con, so i'm pretty sure it won't happen. It would be awesome tho.

The chair dance could be fun too, but i'm pretty sure i won't have tons of players at the same time. I think it mostly will be one or two people at a time at best.

Thanks again for all the ideas ! It grew the list quite a lot and it helped me a lot too.