Unless there is another effect increasing its toughness, it will be put into its owner's graveyard as a state-based action
A 3/4 with flying and haste for six mana, when Olivia attacks, you can put a creature from your graveyard onto the battlefield, tapped and attacking
Keeper of the Accord If youre asking 4 mana for a mana ramp effect, the card in question has to pay off in a big, big way, as ramp often needs to smooth out early land drops and is sometimes critical for getting you off the ground in a game of MTG
5 Path to Exile Instant Path to Exile returns in this set and is a one-mana creature removal spell
Lets take a look at some other top players that compliment Prosper, Tome-Bound
KYLOXS VOLTSTRIDER A very interesting way to reuse some spells