Can Borngray move 15ft, misty step (bonus), multiattack (action), move 15ft away and use shield spell (reaction) if targeted?
@sn0wravenOr does using bonus action to cast misty only leave him the option of a cantrip with a cast time of 1? Casting a bonus action spell does preclude casting a reaction spell on the same turn.
— Jeremy Crawford (@JeremyECrawford) October 21, 2014
That is Rules as Written, and I never put it together despite the rules being clear, I always assumed things like AoO and reactions took place on other peoples turns and were separate from the limitations of of one spell/one cantrips limitations. However, I will continue to allow it in my games and I also allow some higher level spells like healing word to work too.
A Reaction can occur at any point during anyone’s (including your own) turn, as long as you have a Reaction “slot” available (as it were) and the conditions meet the specifics of the Reaction in question.