For more information on meld cards, see the Eldritch Moon mechanics article (https://magic.wizards.com/en/articles/archive/feature/eldritch-moon-mechanics-2016-06-27).

The set of creatures affected by Chittering Host's triggered ability is determined as the ability resolves. Creatures you begin to control later in the turn won't get +1/+0 or gain menace.

If a card in a player's graveyard has in its mana cost, X is considered to be 0.