Breeding

Breeding is a method by which two pets may be used to produce more. The dam will become pregnant (a word used regardless of the species of the pet) for exactly 120 hours. This is the equivalent of five days, but does not rely on rollover to measure the passage of time. Once pregnancy is complete, the young pet(s) will automatically appear in the owner's territory, sorted directly below the active pet.

Requirements
In order for two pets to succesfully breed, all of the following must be true:

If the receiving player only has one free space in their territory, but the pair produce twins or triplets, the additional offspring will still appear as normal, occupying temporary space.

Receiving Player
If the player breeding the pets wishes to ensure the offspring go to someone else, they can type that recipient's username into the options box at the bottom of the breeding page. This most often comes into use when breeding via classifieds, as this allows one player to breed with a pet not currently in their territory (for a fee).

By default, the receiving player is always the one carrying out the breeding. This means it will be the player who made the request via classified, or else the player who owns both parents. This applies even if they sell a pregnant pet - meaning that if a player buys a pregnant pet, they will own only the pet they bought, not its future offspring; those will go to whomever was set via the receiving player box, even if that box was left empty(default).

Potions
A choice of potions may be applied to a breeding before it is confirmed to influence the outcome - that is, to increase the chances of, or in some cases guarantee, more desirable offspring. Upon confirmation of breeding, the potion is consumed.

In addition, two more potions exist which can effect the outcome of a breeding, but usually by permanently changing one or both parents.

Fertility
A pet's fertility determines their ability to produce more than one offspring at a time. Specifically, the chances of twins or triplets. As fertility is a stat, it is hereditary. The minimum value is 0 and the maximum is 100. All first generation pets begin with a fertility of 0; the only way for a pet to gain fertility is via potion or heredity.

Fertility can be thought of as a percentage, representing the overall likelyhood of multiple offspring.

When two pets breed, their fertility is averaged, and it is that average which determines the pair's ability to produce twins or triplets. Although the average is exact, it's unknown what happens in the instance of a non-integer.
 * Averaging

This average is then divided by two to determine the chance as a percentage of twins. This means two pets with a fertility of 100 have a 50% chance of producing twins; one pet with a fertility of 10 and another at 60 has a 35% chance of twins.

The same average is also divided by ten to determine the chance as a percentage of triplets. Two pets with a fertility of 100 have a 10% chance of producing triplets; one pet with a fertility of 10 and another at 60 has a 7% chance of twins.

The offspring of a pair will inherit a rough average of that pair's fertility. The number may not be an exact average, as indicated by text at the bottom of the knowledgebase page on breeding items.
 * Heritability

This means the offspring of a pair whose fertility is both 100 will have a fertility stat of 100; the offspring of a pair whose a fertility are at 10 and and 60 will inherit a fertility of 35.