Mix 2 parts potato starch with 1 part water
Stir until the mixture becomes thick and slippery
Add more starch if it is too runny
Add more water if it is too stiff
Use tapioca starch instead of cornstarch in the same ratio
Use arrowroot powder instead of cornstarch in the same ratio
Use rice flour for a thicker, less stretchy version
Use wheat flour for a simple substitute, adjusting water slowly
Use baking soda mixed with a little water for a paste-like version
Use finely ground oats blended with water for a textured version