You will need some shuffle, mill and/or scry effects to take full advantage of the Library but most combo orientated decks should be able to manage that
Teval, Arbiter of VirtueTeval, Arbiter of Virtue Giving all your spells Delve is a huge advantage to have, but it comes at a great cost of losing life equal to the mana value for each spell cast
The couple that are base green and want some ramp value the green ramp effects not dissimilar to The Rock or traditional Green Ramp decks
Estimated Prices Come Launch It's worth noting that these are pre-order prices if fans were to purchase them as singles from resellers
Rounding out the list are some noncreature spells with strong Legends synergy, mostly ramp like Leyline Immersion and Relic of Legends but also other stuff like board wipe with Urza's Ruinous Blast and mass reanimation with Primevals' Glorious Rebirth
Cards like Kenrith, the Returned King or The Ur-Dragon demand multiple colors of mana