The ability is granted as part of the copy effect, which means it will be removed by any effects that would remove abilities regardless of when the effect was created.
Unstable Shapeshifter
If an Unstable Shapeshifter is on the battlefield when another Unstable Shapeshifter enters, the first one gets the second one's triggered ability, so it will copy the next creature that enters twice. It will only do so the next time a creature enters, because the second "becomes a copy" effect to resolve will erase the extra triggered ability.
When it changes "shape" to a new creature, any "enters" abilities of the creature do not trigger.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Terese Nielsen
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
