Twinmaw Stormbrood

If an Omen spell has one or more targets and all of those targets are illegal when the spell tries to resolve, it won’t resolve. None of its effects will happen, and it will be put into its owner’s graveyard. It won’t be shuffled into its owner’s library.

If a spell is cast as an Omen, its controller shuffles it into its owner’s library instead of putting it into its owner’s graveyard as it resolves.

If an Omen spell is copied, that copy is also an Omen and is shuffled into its owner’s library as it resolves. Its owner still shuffles their library, but the copy ceases to exist as a state-based action.