Mayhem represents an alternative cost that can be paid to cast a spell from your graveyard if you discarded the card with mayhem that turn. You must pay any additional costs the spell has.
Carnage, Crimson Chaos
If the returned creature can't attack for any reason (such as being tapped or having come under your control that turn), then it doesn't attack. If there's a cost associated with having it attack, you're not forced to pay that cost, so it doesn't have to attack in that case either.
If a card in a graveyard has {X} in its mana cost, X is 0 when determining its mana value.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Leinil Francis Yu & Sunny Gho
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
