| Hawktitan |
Summoner would by far be your best best. If you wanted to make him a horror rather than just summon one then use the Synthesist archetype.
Use lots of tentacles and bites. I'll design something like this if you are interested.
As far as races go you won't beat a half-elf in terms of power. A Fetchling with the Shadow Caller Summoner archetype seems appropriate though for flavor.
| lemeres |
Anything Qlippoth related would be appropriate. That is the type of fiend that includes a lot of the star fish aliens and the original form of certain demon lords like Cyth-V’sug, Dagon, Jubilex, Mazmezz, Yhidothrus, and Zevgavizeb, and other names that have apostrophes or too many weird consonants. Dagon in particular is good since it was in one of Lovecraft's short stories, and it has enough tentacles to suffice. From what little I could gleam, the actual Dark Tapestry is too dark/mysterious/copyrighted to go into much detail. Their CR are too much to even list, like with most gods.
Qlippoth spawn tiefling with a heaping helping of the unusual physical traits from the varient table would work. They get a penalty to INT though, so Sorcerer, cleric, or oracle might be best. See how easily you can summon things not meant for mortal eyes. You'll get the full Lovecraft experience when they eat your face off.