Concept: The deck a magician uses has to be connected to the spectator in order for this to be able to perform.
More:
Depending on the spectator for which you are performing, the magician is able to execute some effects, while others just don't seem to work. This can either be interpreted by the spectator just not reacting to these effect (for him they just feel normal - because these magic effects are part of him/her) or the magician not being able to execute them technically.
The will of the spectator is reflected through the hands of the magician, in the way in which he performs, the patters which he uses, the emotions he sends.
If connected to a very mentally powerful spectator (and this can be a stooge), the audience member can end up manipulating the hands of the magician himself/herself.
Different approach:
What the magician performs reflects visually/aesthetically on the spectator's clothes, eyes, behavior, etc.
A color change would change the viewers clothes, or teeth color, iris, skin - you name it.
If you say "Let's imagine the card you selected is your wallet" and then execute a steal of the card from the deck, at the same time you are also stealing the spectator's wallet. If you are to switch this "wallet" card with a "tie" card, literally, the two change on the spectator's body and he looks down to discover his wallet tied around his neck and his tie in his pocket.
A world
In this world, when spectators go to a game, be it baseball or basketball, each one of them must connect to a device. This device is connected directly to each player. In reality, the players aren't the one's playing, but rather the fan bases are the one's battling against each other, the accumulated strength of their will influencing how their team plays and reacts to the other team.
When folks go to theater plays, what they want to happen influences what the actors are performing on stage. If most of them wish for the actors to kill each other, it will happen without this being able to be stopped by the actors on stage.
You can have stages where not everyone can connect to this device, but rather just a team of carefully chosen individuals can.
Before designing a product, companies to a test show, where they bring hundreds of individuals, connect them and ask what would they like to see next from their company. The product that comes out of their mutual will is what the company makes.