When this enchantment enters, if you cast it, destroy all nonenchantment creatures.
Whenever this enchantment or another enchantment you control enters, until end of turn, this enchantment becomes a legendary 6/6 Nightmare God creature with menace and deathtouch. It's still an enchantment.
(28/07/2023)
A noncreature permanent that turns into a creature can attack, and its abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.
(28/07/2023)
You can't cast an Aura with "enchant creature" targeting Cacophony Unleashed unless it's already a creature before you cast that Aura. When Cacophony Unleashed stops being a creature, any such auras will be put into their owners' graveyards.
