If a cost to cast a spell includes revealing a card, that card remains revealed from the time the spell is announced until the time it leaves the stack.

If an effect refers to a “[subtype] card,” it refers only to a card that has that subtype. For example, Teeming Dragonstorm is a card that cares about Dragons and features Dragons in its art, but it isn’t a Dragon card.

Effects that say “If a [quality] was beheld” only care if a card of that quality was revealed or a permanent you control of that quality was chosen. No matter what happens to that card or permanent after that, it was still beheld, and any additional effects that depend on that card or permanent being beheld will still happen.

If a card in your hand is already revealed (perhaps because it was revealed to pay a cost of a spell that’s still on the stack or due to the effect of a card like Telepathy), you may reveal it again to pay the cost of another spell or ability that requires you to reveal a card from your hand.