Resources are needed to make progress further into the game, and are collected by four different types of gatherers.
Twigs are one of the two main building materials, used in almost every construction. It can be gathered by Twig Snappers. You can fling varying amounts in for focused damage.
Pebbles are as important as twigs in construction. It is gathered by Pebble Shiners. You can fling varying amounts in for spread damage.
Putty is used in some construction, but usually is used for unlocking and upgrading monsters. It is gathered by Putty Squishers. It can be flung in to speed up monsters and give them extra armor for a short time.
Goo is special- it is only used in the production of monsters. It can be gathered either by Goo Factories or by juicing monsters.