Memory's Journey

"Flashback [cost]" means "You may cast this card from your graveyard by paying [cost] rather than paying its mana cost" and "If the flashback cost was paid, exile this card instead of putting it anywhere else any time it would leave the stack."

To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.

If no cards were targeted by Memory's Journey or if all the targeted cards are illegal targets by the time Memory's Journey resolves, the targeted player will still shuffle their library.

If the player is an illegal target by the time Memory's Journey resolves, the spell will have no effect, even if the cards are still legal targets. This is because a spell can't make an illegal target (the player) perform any actions (such as shuffling their library).

If you cast Memory's Journey with flashback, it won't be in the graveyard when you choose targets. It can't target itself.

Any of the targeted cards that are illegal targets by the time Memory's Journey resolves aren't shuffled into their owner's library.

You don't have to target any cards when you cast Memory's Journey, but you must target a player.