Display custom fields in pop up

Hi,
what I want to do the following:

When viewing a post (which is information about a game), there should be a button/link/whatever that says “show game details”

When the user clicks on this button, a pop-up will appear, showing the game details (which are custom fields) for that game.

I think the way to do this is to have a game-info.php template, which can accept queries such as: game-info.php?game=mario

so…any advice ?