@JeremyECrawford Is a caster aware that a spell (e.g. Zone of Truth) has no effect on a raksasha?

— Mark Cogan (@marqcogan) December 5, 2015

The characters' knowledge about monsters is up to the DM, considering the characters' experiences & research. #DnD https://t.co/xwXCQLwyiT

— Jeremy Crawford (@JeremyECrawford) December 5, 2015