Cheapest priced copy (Commander Masters): $1.49 at Card Kingdom, near mint, their price list as of .
Cacophony Unleashed 
Enchantment · Rare · Commander Masters · #730
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.
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
2 printings · $1.49 to $4.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 730 | Rare | $1.49 | — |
| Commander Masters | 761 | Rare | $1.49 | $4.49 |
2 rulings from Wizards of the Coast
- 28 July 2023A noncreature permanent that turns into a creature can attack, and its {T} 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 July 2023You 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.