Originally announced for the 64DD, Animal Leader was developed as part of Nintendo's Marigul Management scheme, giving small developers the opportunity to develop original games with a first-party publishing contract. With the 64DD's low sales, game development was put on hold and ported to the Gamecube by Intelligent Systems. Nintendo published the game in Japan, but low sales led to the game being published in the United States by Atlus under the title Cubivore: Survival of the Fittest.
In a land populated by cube-shaped animals, the Killer Cubivore sits at the top of the food chain, absorbing the "Wilderness", the essence of the land, and draining life from the world. Your aim is to climb to the top of the food chain and challenge the Killer Cubivore, restoring the Wilderness to the world.
Your Cubivore can mutate based on its color, intensity and limbs. The color determines the species, while intensity provides additional strength. Limbs are appendages that can be torn off by fighting other Cubivores, and added to your own Cubivore. The ultimate aim is to reach 100 mutations total in order to produce offspring strong enough to take on the Killer Cubivore.
When facing another Cubivore, you have to attack it, weaken it, and tear off its limbs. When you eat a limb, your Cubivore is healed a little, absorbs the color of that limb, and mutates if possible. Larger Cubivores have a special limb called "Raw Meat", which gives you a special ability if eaten.
If you come up against a Cubivore too powerful to fight, you have to enter the Love Tunnel where is can mate and produce a new generation of Cubivore with an extra limb. As you gain more mutations, you have more mating options, providing greater choice in how the next generation will appear. Any Cubivore you have acquired or bred are saved to the EZ Mutate catalogue, and you can switch to that mutations at any time when you have the right number of limbs.