Spike stone

The stone he put in its place looked almost exactly like Jon's stone, but it wasn't. It was the Spike Stone. It worked in exactly the same way as the previous stone - except this stone's wishes are reversible, and each time a wish is granted spikes jutted out of the stone. Because each wish required a payment of blood from the wisher. Whats more, any wish made on the Spike Stone requires a corresponding amount of blood based on the size of the wish, but it could not kill the wisher from blood loss,