Corpse Cobble

You must still follow any timing restrictions and permissions, including those based on the card's type. For instance, you can cast a sorcery using flashback only when you could normally cast a sorcery.

You may choose to sacrifice no creatures to pay the additional cost. If you do, you'll create a 0/0 Zombie token. Unless something else is raising its toughness, the token will subsequently die, but any "enters the battlefield" or "dies" triggered abilities will still trigger.

To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.

If a card with flashback is put into your graveyard during your turn, you can cast it if it's legal to do so before any other player can take any actions.