If the target card is an illegal target by the time Cling to Dust tries to resolve, the spell won’t resolve. You won’t gain 3 life or draw a card.

If you cast a spell with its escape permission, you can’t choose to apply any other alternative costs or to cast it without paying its mana cost. If it has any additional costs, you must pay those.

To determine the total cost of a spell, start with the mana cost or alternative cost you’re paying (such as an escape cost), add any cost increases, then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was and no matter whether an alternative cost was paid.

Cling to Dust can target one of the five cards you’ll exile to pay its escape cost. In this case, the spell won’t resolve.

If the exiled card is a creature card that’s also another card type (such as an enchantment creature), you gain 3 life. You don’t also draw a card.

If a card with escape is put into your graveyard during your turn, you’ll be able to cast it right away if it’s legal to do so, before an opponent can take any actions.

Escape’s permission doesn’t change when you may cast the spell from your graveyard.

Once you begin casting a spell with escape, it immediately moves to the stack. Players can’t take any other actions until you’re done casting the spell.

After an escaped spell resolves, it returns to its owner’s graveyard if it’s not a permanent spell. If it is a permanent spell, it enters the battlefield and will return to its owner’s graveyard if it dies later. Perhaps it will escape again—good underworld security is so hard to come by these days.

If a card has multiple abilities giving you permission to cast it, such as two escape abilities or an escape ability and a flashback ability, you choose which one to apply. The others have no effect.