Whoa. Have never thought of that before.
Combine that with a Silvanshee's Heroic Strength (+8 to strength for 1 minute) and it could do some serious damage.
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Spirit binder wizard archetype could be brutal with this - a familiar with base attack bonus equal to your wizard level. I might have to build something like this...
Alternatively, Eldritch Guardian with Mauler Familiar and a friend who's a Brown-Fur Transmuter.
The fighter stacks EG with Mutation Warrior and a natural-weapon style, and the familiar gains the combat feats the fighter puts towards the natural weapon(s). Make it a human/half-orc/half-elf/aasimar(scion of humanity) fighter and those could even extend to "all natural weapons" due to martial versatility and martial mastery.
The arcanist uses their 9th level power to cast FotD III on the familiar, for a standard bonus of +12 (net of +16 due to tiny->small transition). Combined with the +9 the mauler normally gets, this is a total of +25 over the normal for such a creature. Even a Str 1 familiar now punches pretty hard with an attack retinue of +28/28/28/23/23/23 at 20th level with no gear. Not too shabby for a sidekick with one buff active. A fox would be +4 over those numbers due to higher base strength (9 as a tiny familiar). It could be argued that Battle Form's +2 still works when polymorphed, but I won't tread that path over a +1. Give it a +5 AomF and a belt of Str + 6 and you're really rockin' (+32/32/32/27/27/27 with power attack for over 40 damage on primaries, a bit under 30 on secondaries).
Sadly, that still likely leaves the familiar on mook duty (their AC and saves are nothing special), but even that's pretty impressive for what would have otherwise been viewed as little more than ornamentation.
(You could also take Spirit's Gift to squeeze out a bit more strength. 42 strength on a familiar?! Yeouch! And as long as we're talkin' 20th level, the arcanist technically grants yet another +2 to str at that level due to their capstone. 44! Get a Skald in that party and now it's 50!)
EDIT: It may even be possible for the fighter to give his Mutagen to the familiar via Share Spells. That's another +8 (total 58). This is because of a line in tumor familiar which may be an expression of a general rule: "An alchemist’s extracts and mutagens are considered spells for the purposes of familiar abilities like share spells and deliver touch spells". I wouldn't try this one without asking first, though :P.