wotc
If Ancestral Vengeance causes the enchanted creature to have toughness 0, that creature and Ancestral Vengeance will be put into their owners' graveyards. The enters-the-battlefield ability will still apply.
If Ancestral Vengeance causes the enchanted creature to have toughness 0, that creature and Ancestral Vengeance will be put into their owners' graveyards. The enters-the-battlefield ability will still apply.
If the creature targeted by Ancestral Vengeance's enchant creature ability is an illegal target as Ancestral Vengeance tries to resolve, Ancestral Vengeance won't resolve. It won't enter the battlefield, and its enters-the-battlefield ability won't trigger.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Yohann Schepacz
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.