It depends a lot on the other parent I'd say, so finding a template for 'any' pairing is going to be hard.
As an example, if your troll half-devil half-dragon character ends up having a child with a dragon, the child is likely to have the half-dragon template instead of draconic, same with a devil and half-fiend. As lackluster as Draconic might be, it's the most realistic template for your child to get with any non-draconic parent. Half-troll is obvious for any non-troll pairing
So basically, any non-draconic, non-fiendish, non-troll parent will result in the child having the half-troll, draconic and fiendish templates. Unless shenanigans were involved in the birth and/or the other parent has an exotic race and/or template herself.
If you're looking for something else, Dragon Mag 350 had a number of different 'mutation-based templates', which were basically creatures tainted by magical pollution in one way or another. Any creature born to a parent with a high number of magical bloodlines/templates is likely to develop a mutation as a result of the intermixing, and likely unstable, DNA/magical energies. The Arcane-Blood and Stoneboned templates are the most likely, but it's also possible the mixture of troll/fiend/dragon blood creates a Corrupted off-spring, especially if your troll, or the other parent, has spent any time in toxic landscapes or places of dark/evil/fiendish magic/energy, or has been experimented on in quite heinous ways.
That's about it though, all I can think of, hope it helps
