Additional cards were available in sample decks and Deckbuilder's Toolkits only. They are numbered X/Y, with X > Y and Y the number of standard cards in the set. Sample decks of all languages are confirmed.
Magic 2015 (15 cards):
Aegis Angel
Cancel
Centaur Courser
Divine Verdict
Furnace Whelp
Garruk's Packleader
Inspired Charge
Mahamoti Djinn
Nightmare
Seismic Strike
Sengir Vampire
Serra Angel
Shivan Dragon
Terra Stomper
Walking Corpse
Magic Origins (16 cards):
Aegis Angel
Divine Verdict
Eagle of the Watch
Fiery Hellhound
Flesh to Dust
Into the Void
Mahamoti Djinn
Mind Rot
Nightmare
Plummet
Prized Unicorn
Sengir Vampire
Serra Angel
Shivan Dragon
Terra Stomper
Weave Fate