Modern Horizons
Modern Horizons contains 254 cards (5 snow-covered basic lands, 101 commons, 80 uncommons, 53 rares, 15 mythic rares), and includes randomly inserted premium versions of all these cards. In addition, there is a Buy-a-Box card numbered #255/254. This set introduced new cards into Modern without them ever being legal in Standard. It contains 209 new cards and (excepting the snow basics) only reprints which previously weren't legal in Modern.
Modern Horizons was originally dubbed as "Timespiral / Planar Chaos 2" in concept due to set complexity. Mark Rosewater has called it a a "love letter" to the Time Spiral block. It isn't an entry level set because of its many returning mechanics. There was no story support for the set.
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