Generations/Lore/Race Crosses
This page will cover how to create a crossbreed, and randomly calculate any offspring.
Attributes
The product of an interspecies pregnancy should have attributes that fall between the parents' abilities. For example: If one parent has a Body of Weak (3) and the other a Body of Exceptional (8), the child should have an attribute of 3-8. Feel free to do this randomly for children born during the story if you think it would be fun. (There's no way I can tell if you did this, but it is what I will be doing.) Rarely, the child can exceed their parents or be weaker than their parents. If doing this randomly, give them a 5% chance of having an attribute 1 lower than that of the weakest parent, and a 5% chance of having an attribute 1 higher than the strongest parent. (Using a d20 that would be a decreased attribute on a roll of 1 and an increased attribute on a roll of 20.) For incestuous offspring, increase the chances of mutation to 20% on the low end and 10% on the high end (1-4 and 19-20 respectively on a d20).
Abilities
The product of an interspecies pregnancy has a 50/50 chance of inheriting each of the parent's abilities. This is not a genetically sound system, but I'm not writing up a race sheet for each race cross combination into infinity. Any abilities gained by physical means should affect the child's appearance (e.g. if a child has winged flight, they should possess wings, etc.). If both parents have the same ability, the child automatically inherits that ability.
Abilities are inherited one at a time. It isn't all or nothing. Each ability has a chance to be inherited separately, even if they derive from the same source.
Some abilities are inherited in a specific manner; for instance the merfolk's Water-breathing ability automatically becomes Air & Water Breathing in crosses with air breathers. In this case use the inheritance specified in the race description.
Aging
The product of an interspecies pregnancy ages at a rate that is an average of the parents. It should be calculated by the following formula (a+b-1)/2 where a and b are the age modifiers of the parents. For instance: an elf has an age modifier of 10, and a human has an age modifier of 1. A 1/2 elf 1/2 human would have an age modifier of (10+1-1)/2=5. So the half elf at 25 would be the equivalent of a 25/5=5 year old human. Another example: a dragon has an age modifier of 25, and an orc has an age modifier of .75. A 1/2 dragon 1/2 orc would have an age modifier of (25+.75-1)/2=12.375. So the half dragon at 25 would be the equivalent of a 25/12.375=2.02 year old human.