Old and newer fiction books lookup
I can't for the life of me figure out what these books were, and I hope you all can help me again.
Starting with the newer one: a guy gets sent back in time I think, but he knows how to make gunpowder and stuff. He survives being attacked and pledges himself to a god, which is a god that doesn't normally allow that kind of thing. There are mages and monsters and mages are rated on a scale. Mage/fighters give no shits for defense and just beat folks til one mages shield gives out. Monsters can also take levels from a person. Something about boiling down brains and distilling the mage thing. The book ends with the guy being tortured after winning a battle and learning that the powers that be allow awful losses to give more brain boiling stuffs.
The tougher one: Young adult novels where a group of plucky kids got sent into the past and then witnessed folks being sacrificed to a god. Before being sacrificed they escaped somehow and murdered Quetzalcoatl. There were maybe 3-4 books in the series at the time.
Shot in the dark but it would be cool to know.