Been having some issues with these lately related to the logic discontinuity and differences in how a particular GM applies them.
Knowledge religion (also planes, dungeoneering, nature, and arcana) - PC can roll DC=15+CR check to learn about monsters weaknesses. How exactly is the PC supposed to know that this in particular is an advanced, feral, champion gray render with 8 levels of monk to know what abilities it has. I don't care that he rolled a 20 with a +27 skill modifier. It is a unique creature. That seems way too powerful. However, a different GM says all you can find out about it the base gray render abilities. Of course he doesn't use anything without a template and/or class levels. So it is again a virtually useless skill.
You recognize the Grey Render for what it is, by the way it moves or perhaps being slightly larger you can determine it is advanced, the foaming of the mouth makes it feral and champion (is champion a template?) might be picked up by a subtle thing that someone not as well versed in Grey Renders might not have known?
Nothing says you would recognize its class or level.