Soot Puff
From Everafter Falls Wiki
Soot Puff is a special type of critter what randomly spawns on the main map locations and can be caught with a Bug Net. Once caught, a Soot Puff can be donated to the tank inside the Museum for some unique rewards or placed into a Soot Grower to increase its size over time.
Every Soot Puff has a size randomly assigned to it when it spawns; that size is added to the Museum's Soot Puff size when donating and used to calculate the reward the player receives. The size of a Soot Puff can be increased by placing it into a Soot Grower that adds a fixed value to its size every morning.