I've been trying to find the best set of rules to build crazy monsters I have models for, but no rules for (*cough* old warhammer models *cough*) and I finally found a set that seem reasonable and should (?) be fairly balanced.
Normally (though not always) NPCs that I find online are CR: <Class_Level>-1; so I used that with the Eidolon rules (but with just the Eidolon and not the Summoner.)The first Eidolon I created seems alright in that vein, but may be a bit much (because honestly, the Eidolon rules seem a bit OP.) It certainly seemed way easier than standard build-a-monster rules though.
Any thoughts on continuing to use these for "build a monster" general skeleton?
I would like to direct you towards Pathfinder Unchained's simple monster creation rules.
I find them to be both robust and easy to use.