As an additional cost to
castTo cast a spell is to take it from the zone it’s in (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. A player may cast a spell if they have priority. See rule 601, “Casting Spells.”
To cast a card is to cast it as a spell. (CR 701.5) this spell,
exileTo exile an object, move it to the exile zone from wherever it is. See rule 406, “Exile.” (CR 701.13) six cards from your graveyard.
FlyingFlying is an evasion ability.
A creature with flying can’t be blocked except by creatures with flying and/or reach. A creature with flying can block a creature with or without flying. (See rule 509, “Declare Blockers Step,” and rule 702.17, “Reach.”)
Multiple instances of flying on the same creature are redundant. (CR 702.9)
At the beginning of each opponent's upkeep,
manifest dread“Manifest dread” means “Look at the top two cards of your library. Manifest one of them, then put the cards you looked at that were not manifested this way into your graveyard.” See rule 701.40, “Manifest.”
An ability that triggers whenever a player manifests dread triggers after the process described in rule 701.62a is complete, even if some or all of those actions were impossible. (CR 701.62). (Look at the top two cards of your library. Put one onto the battlefield face down as a 2/2 creature and the other into your graveyard. Turn it face up any time for its mana cost if it's a creature card.)