I recently added Witch to my horrendously multi-classed Fighter and found this little brain teaser. I had adopted a Blue Russian (cat) as my linked familiar whom I can cast self-altering spells on, including Long-Arm. Seeing as my partner is Quadrupedal, I imagine something like this happening during the effects of the spell
Anyway, would my cat be considered a medium creature or be a tiny creature that just so happened to stand 5'3"?
The table for creature size contains a a footnote at the typical height/length column, saying:
These values are typical for creatures of the indicated size. Some exceptions exist.
As the spell Long Arm does not say anything about creature size, I would assume that your Blue Russian is one of those exceptions and would therefore count as a tiny creature with reach it's reach increased by 5", interpreting the rules.
This also makes sense otherwise, as the natural weapon damage of the cat would increase if it would be of a greater creature size.
In this particular combination, I might consider to think of an appropiate houserule, but this is just my thought, e.g. long-arms on the cat works the same as if it would be affected by enlarge... or alike.
This is a weird one, to be sure. Unfortunately I don't have much in the way of RAW to answer but this is how I've logic'd it out.
Long-arms cat would have a reach of 5', that much we know for sure.
Considering its body size and therefore the size of its claws hasn't changed I'd argue it would still do damage as a Tiny creature.
Also considering its body size I'd argue it would still have the size bonus to AC of a tiny creature. Cutting its silly legs out from under it probably wouldn't do as much damage as stabbing its body.
(Honestly I imagined long-arms cat as only having long forelimbs, like some kind of stretchy Egyptian sphinx)
