Keyword: Fathomless descent

Fathomless descent — When Chupacabra Echo enters, target creature an opponent controls gets -X/-X until end of turn, where X is the number of permanent cards in your graveyard.

Fathomless descent — Return to the battlefield target nonland permanent card in your graveyard with mana value less than or equal to the number of permanent cards in your graveyard.

As an additional cost to cast this spell, discard a card or sacrifice a permanent.
Fathomless descent — Souls of the Lost’s power is equal to the number of permanent cards in your graveyard and its toughness is equal to that number plus 1.

Fathomless descent — All creatures get -X/-X until end of turn, where X is the number of permanent cards in your graveyard.

Fathomless descent — All creatures get -X/-X until end of turn, where X is the number of permanent cards in your graveyard.

Fathomless descent — Return to the battlefield target nonland permanent card in your graveyard with mana value less than or equal to the number of permanent cards in your graveyard.

Enchant creature or Vehicle
When Song of Stupefaction enters, you may mill two cards. (You may put the top two cards of your library into your graveyard.)
Fathomless descent — Enchanted permanent gets -X/-0, where X is the number of permanent cards in your graveyard.

As an additional cost to cast this spell, discard a card or sacrifice a permanent.
Fathomless descent — Souls of the Lost’s power is equal to the number of permanent cards in your graveyard and its toughness is equal to that number plus 1.