What are the sources on this summons list? As in I don't know what these letter/number combos mean.
Table: Summon Monster II (Alternatives)
2nd Level Alternatives Subtype(s) Source
Akata — AP64
Elk* — AP32
Grig2 — AP50
Hell hound Lawful, Evil AP29
Merfolk* — AP38
Reefclaw — AP55
Venomous snake* — AP42
^ooo that didn't come out like I typed it.
Those are all from Adventure Paths, and the number relates to the book number. If you go to this page: http://paizo.com/pathfinder/adventurePath and scroll down a bit, you can see which APs relate to which numbers, and can figure out the book from there.
Are any of the summons conditional at you/ya'll know of?