Can be achieved by placing different Magic style furniture pieces, it doesn't matter what type (can be kitchen, chairs, art) as long as it has the Magic indicator in the game.
More Magic furniture will unlock while researching different things at the decoration shrine and you will also be able to unlock some Magic Furniture via friendship levels.
The game will state if you already have 1 of an item and that the stats won't go up, i.e.; have 2 of the same Magic furniture of Magic: 2 stat, is not 4 stat, it's 2 stat.