Crumb and Get It

For permanent spells with gift, an ability triggers when that permanent enters if the gift was promised. When that ability resolves, the gift is given to the appropriate opponent.

If a spell for which the gift was promised is countered, doesn't resolve (perhaps because all of its targets are illegal), or is otherwise removed from the stack, the gift won't be given. None of its other effects will happen either.

You can't pay a gift cost more than once.

Some instant or sorcery spells require alternative or additional targets if the gift was promised. You ignore these targeting requirements if the gifts aren't promised for those spells. On the other hand, you can promise a gift for a permanent spell even if you won't be able to choose targets for an enters ability of that permanent once the spell resolves.

If you copy a spell for which the gift was promised, the gift was also promised to the same opponent for the copy. If a card or token enters as a copy of a permanent that's already on the battlefield, the gift isn't promised for that new permanent, even if it was promised for the original.