Rockhorns beasts:
- until he is 5th level in the class, he has only one companion and he will be 4th after this level (and gain monstrous flank) - I don't think bloodline gives you real level effects. It only affects those things calculated on level and not real class features. It would be overpowered since it applies to all classes.
- what bloodline levels do is help mitigate the level loss because my companion at 5th would be like 3rd level and not 1st level and Spritewing gain additional ability boost and Devotion
What I asked on discord was to temporary replace Spritewing with a blink dog, both to establish story line for the deeper link that develops at 5th (extra companion) and to leave flying creature out of the dungeon. But if you're fine with it - as you said, it is dungeonbred - I can take Spritewing no problem. Only reason I asked is because you seemed reluctant to have a flying creature in the dungeon.
Complete list of monsters available by the book:
1st level: ankheg, blink dog, giant eagle , giant owl, hippogriff, krenshar, otyugh owlbear, pegasus, worg
3rd level: Digester, girallon, manticore, winter wolf
5th level: chimera, wyvern
7th level: chuul, destrachan, dragonne
9th level: behir, gray render, yrthak
If you want to add or replace things, go ahead
I'll be good and won't force poor people of Bluffside to tolerate otyughs or chuuls in their midst