Not half mixed species character creation
So mixed species advancement is for individuals who are 1/2 species X and 1/2 species Y. However, I have to ponder what about individuals who are 3/4 species X and 1/4 species Y, and other smaller fractions? How does one create a template for those individuals?
For instance what about 3/4 human, and 1/4 trill?
If it's not too late to add my two-cents. . .
I seem to recall this being handled in the core books. It worked the same as for half-n-half characters. Take 3/4 of the dominant species Attributes and 1/4 of the none dominant and the Skills of the species the character was raised as.
So for your Human/Trill example; pick four Attributes from the Human Template and one from the Trill. Being 3/4 Human I imagine the character was raised on Earth or an Earth dominant colony so the character would get the Skills/Traits from the Human Template.