I just experimented a bit in MTGA and I don't understand how this situation resolved and why:
I have a Kargan Intimidator on the field and play my Glorious Protector. In response to the etb trigger, the Intimidator makes the Protector a Coward. Then when the trigger resolves, I choose the Protector (now only a Coward and not an Angel) and the Intimidator (among other things) for exile. And they sure are all exiled, but while the other creatures return immediately, the Protector is now trapped in exile. I would have expected it to either return with the rest, or no creature being exiled in the first place.
In this case, the effect of Glorious Protector's triggered ability "cause[s]" Glorious Protector and the other chosen creatures "to change zones 'until'" "Glorious Protector leaves the battlefield" (C.R. 610.3). Thus, Glorious Protector, just as well as the other objects exiled this way, will reenter the battlefield "immediately after" that event, and at the same time (C.R. 610.3, 610.3d). C.R. 610.3 applies to any "object" that would change zones "until" a specified event happens, even if that object is the source of the ability that did so, such as Glorious Protector.
I have a Kargan Intimidator on the field and play my Glorious Protector. In response to the etb trigger, the Intimidator makes the Protector a Coward. Then when the trigger resolves, I choose the Protector (now only a Coward and not an Angel) and the Intimidator (among other things) for exile. And they sure are all exiled, but while the other creatures return immediately, the Protector is now trapped in exile. I would have expected it to either return with the rest, or no creature being exiled in the first place.
edit: sorry for the typo, I meant MTGA not MTGO.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
Thus, this is an error in Magic Online.
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
By the way, C.R. 610.3b also doesn't apply here since Glorious Protector didn't leave the battlefield before it was exiled by its own ability.