Protean Thaumaturge

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.

Wotc — January 24, 2020

If an enchantment creature enters the battlefield under your control, Protean Thaumaturge’s ability can target it.

Wotc — January 24, 2020

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.

Wotc — January 24, 2020

If Protean Thaumaturge copies a creature that’s copying something else, it will become whatever the target is copying.

Wotc — January 24, 2020

If something becomes a copy of Protean Thaumaturge, it also has the constellation ability.

Wotc — January 24, 2020

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.

Wotc — January 24, 2020

If an effect begins to apply to Protean Thaumaturge before it becomes a copy of another creature, that effect will continue to apply.

Wotc — January 24, 2020

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.

Wotc — January 24, 2020