Protean Thaumaturge

• WWizards of the Coast2020-01-24
  Official Ruling
  If something becomes a copy of Protean Thaumaturge, it also has the constellation ability.
• WWizards of the Coast2020-01-24
  Official Ruling
  A constellation ability triggers whenever an enchantment enters the battlefield under your control for any reason. Enchantments with other card types, such as enchantment creatures, will also cause constellation abilities to trigger.
• WWizards of the Coast2020-01-24
  Official Ruling
  Protean Thaumaturge’s ability causes it to become a copy indefinitely. It doesn’t expire during the cleanup step or if the target creature leaves the battlefield after the ability has resolved.
• WWizards of the Coast2020-01-24
  Official Ruling
  An Aura spell that has an illegal target when it tries to resolve doesn’t resolve and is instead put into its owner’s graveyard. It doesn’t enter the battlefield, so constellation abilities don’t trigger.
• WWizards of the Coast2020-01-24
  Official Ruling
  If an effect begins to apply to Protean Thaumaturge before it becomes a copy of another creature, that effect will continue to apply.
• WWizards of the Coast2020-01-24
  Official Ruling
  Protean Thaumaturge copies the printed values of the target creature, plus any copy effects that have been applied to it. It won’t copy counters on that creature or effects that have changed its power, toughness, types, color, or so on. Notably, it won’t copy effects that made the target creature become a creature.
• WWizards of the Coast2020-01-24
  Official Ruling
  If an enchantment creature enters the battlefield under your control, Protean Thaumaturge’s ability can target it.
• WWizards of the Coast2020-01-24
  Official Ruling
  If Protean Thaumaturge copies a creature that’s copying something else, it will become whatever the target is copying.

Rulings via Scryfall