Surreal Memoir

If a spell with rebound that you cast from your hand doesn't resolve for any reason (due being countered by a spell like Cancel, or because all of its targets are illegal), rebound has no effect. The spell is simply put into your graveyard. You won't get to cast it again next turn.

If you have only one instant card in your graveyard as Surreal Memoir resolves, that's the one you'll return to your hand.

If you cast a spell with rebound from anywhere other than your hand (such as from your graveyard due to Sins of the Past, from your library due to cascade, or from your opponent's hand due to Sen Triplets), rebound won't have any effect. If you do cast it from your hand, rebound will work regardless of whether you paid its mana cost (for example, if you cast it from your hand due to Maelstrom Archangel).

If you cast a spell with rebound from your hand and it resolves, it isn't put into your graveyard. Rather, it's exiled directly from the stack. Effects that care about cards being put into your graveyard won't do anything.

If you are unable to cast a card from exile this way, or you choose not to, nothing happens when the delayed triggered ability resolves. The card remains exiled for the rest of the game, and you won't get another chance to cast the card. The same is true if the ability is countered (due to Stifle, perhaps).

If you're playing a format involving cards printed earlier than the _Urza's Saga_ set, you may not reorder your graveyard. In this case, you need to be more careful when selecting an instant card at random, perhaps by using dice, writing the names of the instant cards on slips of paper and choosing one of them randomly, or carefully noting the existing graveyard order so you can reestablish it after performing the method suggested above, for example.

Rebound will have no effect on copies of spells because you don't cast them from your hand.

If you're playing a format involving only cards from the _Urza's Saga_(TM) set and later, you may change the order of your graveyard at any time. That means the easiest way to choose an instant card at random from your graveyard is to take all the instant cards in your graveyard, turn them face down, shuffle them, and pick a card. Then you just put the rest back.

If a replacement effect would cause a spell with rebound that you cast from your hand to be put somewhere else instead of your graveyard (such as Leyline of the Void might), you choose whether to apply the rebound effect or the other effect as the spell resolves.

At the beginning of your upkeep, all delayed triggered abilities created by rebound effects trigger. You may handle them in any order. If you want to cast a card this way, you do so as part of the resolution of its delayed triggered ability. Timing restrictions based on the card's type (if it's a sorcery) are ignored. Other restrictions are not (such as the one from Rule of Law).

All players get to see which card you chose at random.

If you cast a card from exile this way, it will go to your graveyard when it resolves, fails to resolve, or is countered. It won't go back to exile.

Surreal Memoir isn't targeted. You don't choose an instant card at random from your graveyard until it resolves. Once you randomly select a card, it's too late for players to respond.

If you have multiple instant cards in your graveyard with the same name, and one of them is being targeted by another spell on the stack or is enchanted (with Spellweaver Volute, for example), you must differentiate them so you know which one (if any) is chosen at random. In that case, it may be better to use dice or another method that allows you to differentiate between the instant cards to choose one at random.