Add instant pudding and 1/2 cup of cornstarch in a medium bowl, then stir to incorporate.
Add the warm water and stir until all the ingredients come together and form slime.
Carefully add the remaining cornstarch to the edible slime.
Once it becomes too difficult to stir with the spoon, use your hands to knead and incorporate the cornstarch.
If the slime is too thick, add a small amount of water until desired consistency is met. If the slime is too sticky, add a small amount of cornstarch until desired consistency is met.