Board Thread:Questions and Answers/@comment-4347663-20140120194348/@comment-4536066-20140120213829

Deeen's suggestion is a good one; delineating a list of traits that could go either way between races and flipping a coin or rolling a die is a good way to be impartial in creating a new crossbreed.

If I had to point to any one thing that makes the difference between a "legitimate" crossbreed and a "sueish" crossbreed, it's whether or not you're careful enough about making sure the character has as many weaknesses as he has strengths. A crossbreed that only inherits positive traits from either parent is a lame crossbreed. (Say, perhaps, the character is able to breathe underwater for a limited amount of time, but also gets a painfully dry throat and cracked, dry skin - eczema maybe - if he doesn't soak in water or drink a couple of gallons every day.)