For two players.
Describe a simple object, and ask your friend to picture it in their head. Give them a moment. Now increase the complexity of the object. Add details. Once they've got that, invent manipulations to perform upon it. Your companion must try to follow along until they can't hold it in their head any more.
For example: picture a grid of blue dots, four by four. Make every second dot green. Extrude the corner dots to cylinders that extend above the plane of the grid. No, a little taller than that. Grow the tops of the cylinders into spheres. Start the central four dots pulsating. Now the spheres are crackling with texture, becoming disco balls instead, and they're rotating a little at the ends of their stalks. Light radiates from the central four dots, and bounces off one of them.
You can add sensations as well but it's definitely weirder so y'know choose your situation / check first. There is a cupcake, bright blue, with bright yellow icing. It gets big, bigger still. You are wearing it like a t-shirt, your legs sticking out the bottom, arms out the side. A spotlight shines on you from the left. You are on an empty stage, and right behind you, you hear someone whispering the word "cupcake", over and over. Each time they do, the stage judders and the cupcake squeezes you gently. From above, a sudden shower of smaller cupcakes, two, three, six, that splat onto the stage around you.
When they can't picture it any more it's their turn to make something up. You want to be describing an object or situation that ramps up in difficulty gradually, but that tips over all of a sudden from perhaps one small tweak into the unimaginable and then it tumbles down, oh-almost-I-think-I've-got-it-no-it's-gone. Obviously this isn't a game you can win but if it is, you don't win it by imagining best, you win it by describing things with enough precision and gradual detail that the house of cards is a really satisfying height when it falls over.
