When you cast a card with Morph face down, it enters the battlefield as a 2/2 colorless, nameless creature with no abilities (CR 702.36d). At that moment, any 'enters the battlefield' (ETB) triggers fire — but only for entering face-down. The card is already on the battlefield from that point forward.
Turning a face-down permanent face up is a special action defined in CR 701.33. It changes the object's characteristics but does not cause it to leave or re-enter the battlefield. Because the permanent never leaves the battlefield, it does not 'enter' the battlefield again, so ETB abilities on the face-up card do NOT trigger when it's turned face up (CR 702.36e).
This also means effects like 'enters the battlefield with counters' or replacement effects that modify how a creature enters do not apply when a morph is turned face up, since no entering event occurs.
Concrete example: You cast Bane of the Living face down as a 2/2. Later, you pay its morph cost to turn it face up. Its triggered ability (which says 'when this is turned face up') fires because it specifically references being turned face up — not an ETB trigger. A hypothetical ETB trigger would NOT fire at that moment.
Key rules: CR 702.36d (face-down permanents entering the battlefield), CR 702.36e (turning face up is not a new ETB event), CR 701.33 (turn face up as a special action).
Unofficial fan resource — not affiliated with or endorsed by Wizards of the Coast. Answers are AI-generated estimates grounded in the Comprehensive Rules and are not a substitute for an official judge. Verify anything match-critical.