Pioneer is the newest MTG format. Like Modern before it, Pioneer was designed as a place for decks to be used after they rotate out of Standard. It includes all main sets since Return to Ravnica.
These cards cannot be used in this format:
Balustrade Spy · Bloodstained Mire · Felidar Guardian · Field Of The Dead · Flooded Strand · Geological Appraiser · Inverter Of Truth · Karn, The Great Creator · Kethis, The Hidden Hand · Leyline Of Abundance · Lurrus Of The Dream-den · Nexus Of Fate · Oko, Thief Of Crowns · Once Upon A Time · Polluted Delta · Teferi, Time Raveler · Undercity Informer · Underworld Breach · Uro, Titan Of Nature's Wrath · Veil Of Summer · Walking Ballista · Wilderness Reclamation · Windswept Heath · Wooded Foothills