The creature phase is similar in gameplay to the cell phase,phase, but there are several important differences. Principally, the environment is now truly 3D. There will be other creatures inhabiting the world and most, if not all, of them will have been created by other players. Creatures will be seeded into the player's environment according to certain factors, in order to retain a balanced ecosystem. The game will also download creatures in relation to how strong the player's creature is. If the player creates a bigger, tougher creature, the predators that are downloaded will likewise be stronger than average predators. Creatures' characteristics are categorized with a 5 star rating system in six areas: Speed, Stealth, Defense, Social, Cuteness, and Attack. The creature also gains the ability to perform actions, such as "Call" and "Jump".

In this stage, the basic goal is the same: hunt food to earn DNA points, reproduce, and avoid being eaten by predators. Unlike the asexual reproduction in the cell phase,phase, the player must now locate a mate. Once the player's creature has laid an egg, it does not hatch right away; scavengers will attempt to steal the eggs and the player must defend them (conversely, the player may steal and eat other creatures' eggs as well, if they can get past their hostile parents). Before the egg hatches, the player will have the opportunity to 'evolve' their creature via the creature editor, which can be done by spending DNA points to buy body parts. When the egg hatches, the player controls a baby version of the creature that spawned it. Aesthetically, this version of the creature will be smaller, with certain features exaggerated such as the head, and have a higher pitched voice. "The Science Behind Spore" video featured a monstrous creature taller than a tree threatening a city, indicating one of the scale possibilities of creatures.

This stage will evolve the creature's social behaviour, as the baby will be making friends and forming its own herd (for herbivores) or pack (for carnivores). Will Wright referred to this as a simplified version of the friend-making mini-game in The Sims. The ultimate goal of the creature phase is to increase the creature's brain capabilities slowly using DNA points. Once they have increased sufficiently, the player's creature becomes intelligent and the player progresses to the tribal phase.phase. Creatures may make friends with other species instead of fighting them.

Species are nameable in the Creature Editor. In the IGN "Evolution" video, the creatures had names such as "Oddy", "Mephistopheles" and so forth.

Strong evidence of flying creatures, unseen since the original presentation of Spore, has been seen in recent hands-on previews. No outright clarification about the status of flying creatures has occurred yet. However, winged creatures may "glide", as creatures created during the Spore Creature Creator revealed. All creatures will be land-based; there will be no marine creatures.

As with the cell phase,phase, DNA Points serve as currency towards evolving, increasing brain size and allowing the player to move into the next phase.

On June 17th, 2008, the official "Creature Creator" was released to the public.