While I know that attack rolls have crit success/fail, my group (and many others, for that matter) allow all d20 rolls to crit succeed/fail. What I want to know is what are the ONLY things allowed to do this, RAW, that is?
RAW 20s and 1s are auto success/failure for only attack rolls and saves. Only attacks ever crit, and then when confirmed. There is no RAW crit failure/fumble.
Actually, 1s on some saves can lead to equipment possibly being damaged, you could call that a crit failure, but the book does not.