What races can gnomes interbreed with?

Question

I know that Tieflings and Aasimar can mate and have offspring with Gnomes. I know that most races native to Golarion (human, elf, dwarf, etc.) can't. Purely for flavor, I'm creating a Gnome academic of some standing who has -- for the novelty and to further her learning -- sought out partners of as many races as possible and had children by them. I'm imagining a large family with siblings who're half gnome and half (devil, demon, azata, garuda, djinn, efreet, etc.)

So... what races do we know can('t) mix successfully with gnomes?

Answer 1

The Book of Erotic Fantasy (a d20 third-party supplement) has a large table detailing the ability to crossbreed between many of the common species. This is a list based on the gnomes' entry. Gnomes are actually one of the most restricted species in the table. They are basically only able to crossbreed with the races that can crossbreed with everyone. As stated by EagleV_Attnam (thanks for bringing it up!), the book is aimed at 3.5 and third-party so it's hardly official but it's likely the closest you'll find.

Conception possible:

• Celestial
• Dragon
• Dryad
• Fiend
• Nymph
• Satyr¹

Conception impossible:

• Bugbear
• Centaur
• Dwarf
• Elf
• Giant
• Gnoll
• Goblin
• Half-Elf
• Half-Orc
• Halfing
• Hobgoblin
• Human
• Kobold
• Lizardfolk
• Merfolk/Triton
• Minotaur
• Ogre
• Orc

^{1. These pairings still allow for conception but at a reduced chance. See page 50 of the Book of Erotic Fantasy for more details.}

Answer 2

Gnomes on Golarion can't interbreed with much in general. From Gnomes of Golarion:

Despite an inability to crossbreed with other races, gnomes’ constant hunt for new sensations means they rarely restrict their liaisons to their own kind.

Gnomes are not a fecund race, and as they originally stem from the deathless realm of the First World, the messy business of breeding is relatively new to them. (...) their families tend to be small (...) As lifelong bondings such as marriage are rare, the fickle arrangements mean that children are seldom a good idea, and sensible gnomes take steps to prevent conception (a favorite method being choosing suitors from other races).

Not to say you can't do it, but Golarion lore says "not really."

Answer 3

Dragons and Outsiders, Seems Like

Dragons and Outsiders appear to be the only explicit creatures I can find that can breed with 'everything'. The Half-Fey template implies fey can bear children to other races, but I can't find any explicit rules on this.

There might be specific monsters that can create children with anything too, but I haven't run across any yet. I think that's a bit politically incorrect sort of thing for Pathfinder.

If you've got backwards compatibility to 3.5e, you get weird stuff like half-golems and half-undead from various splatbooks, most of which spell out how they're made.

I also can't find (despite several assertions in answers and comments) any rules stating that the child of an Outsider and a Mortal comes out as anything BUT one of the half-outsider templates. With Half-Dragon it's entirely explicit that anything a dragon sires comes out half-dragon. Half-outsider it's just heavily, heavily implied.