I couldn't find anything in the FAQs or Errata for a few things about these, and there was nothing too clear in the messageboards I could find:
1. Is Beastform Mutagen a polymorph effect?
Base Mutagen does not appear to be a polymorph effect, even when it creates physical changes (feral mutagen). Other abilities that give similar physical changes can go either way, either being a polymorph effect:
Feral Focus - When a feral hunter uses this ability, her body takes on cosmetic aspects of an animal .... This physical change is a polymorph effect, though the effects of the animal focus are not.
(ACG, 96)
or not being one:Shifter's Blessing - This is not a polymorph ability
(APG, 126-127)
But in both cases it is explicitly stated.2. This is a GM-dependent question, but thoughts on - if (1) is yes, which Alchemist abilities would fall under the polymorph rules as per core rulebook :
While under the effects of a polymorph spell, you lose all extraordinary and supernatural abilities that depend on your original form (such as keen senses, scent, and darkvision) ... You also lose any class features that depend upon form ... Your new form might restore a number of these abilities if they are possessed by the new form.
The rules of the new form are just taking upon animalistic features -
At 3rd level, a beastmorph’s mutagen causes him to take on animalistic features—whether those of an animal, a magical beast, an animal-like humanoid (such as a lizardfolk), or a monstrous humanoid. For example, when the beastmorph uses his mutagen, he may gain a furry muzzle and pointed ears like a werewolf, scaly skin like a lizardfolk or sahuagin, or compound eyes and mandibles like a giant insect
So if it is a polymorph effect, would your new form be just your old form + animalistic features, leaving (ex) abilities like tentacles (which is a suggested for the archtype, which would be odd if it didn't work in mutagen for a mutagen-centered archetype) as part of your new form as well?
3. When the Beastform Mutagen grants Grab or Trip, what are the Grab or Trip abilites applied to? And how would Trample work?