Staminungus

Staminungus are leg-shaped mushrooms that temporarily grant you infinite stamina, both while sprinting and during combat.

Infinite Stamina
This effect will let you run forever while active, though it will not refill your Hunger. If you were Hungry before eating this shroom, you will remain Hungry after the effect ends. However, if you are Hungry and don't have a Beast to eat, you could use these as a small boost to run past enemies or get to the next escalator, if you move quickly enough. It is possible to outrun Screamers and Haters if you can get far enough away, as they will eventually de-aggro after they lose sight of you.

It is no coincidence that these shrooms first appear in Crowley's area in the 20's. They are some of the longest floors in the entire game, and can have multiple different wrong paths or dead ends at the end of very long hallways. Don't be afraid you might "waste" any of these you find along the way, eating them can easily save you some time.

You can try to use this effect offensively during combat, though you may want to eat more than one. Attacking with weapons under this effect will not consume any stamina, however, many of the most stamina-draining attacks are heavy and slow, so make sure you have enough time to pull them off. If you don't want to worry as much about Stamina during a Boss fight, you could eat a couple of these before going in as well.

This effect Stacks, meaning that if you eat multiple of this shroom, the effect duration will continue to increase.