
Reksew_Trebla |

Reksew_Trebla |
The page cites its source right at the top: Pathfinder #67: The Snows of Summer pg. 72
Content from the appendices of AP's has a reputation for being a bit dodgy, so you should always ask your GM before utilizing such content.
That was for the template in general. I’m asking about the source for it being usable with summons, which wasn’t in that book, at least not as far I can see.

Taudis |

Could be a sort of marker noting that it's appropriate for a summon. Entropic and Resolute had that for a while before being something that could actually be applied to a summon iirc.
Going to the Acadamae school from Inner Sea Magic should allow you to pretty freely add Boreal creatures to your list, seeing as they'd be the same CR as their Celestial/Fiendish equivalents and it's specifically marked as appropriate for summoning. The rules for education are a bit... loose but following the book's recommendations for how to gain prestige within your own school you'd be able to add 1-2 Boreal creatures per class level.