Tilonalli's Summoner (121) [Rivals of Ixalan]

Ascend (If you control ten or more permanents, you get the city's blessing for the rest of the game.) Whenever this creature attacks, you may pay {X}{R}. If you do, create X 1/1 red Elemental creature tokens that are tapped and attacking. At the beginning of the next end step, exile those tokens unless you have the city's blessing.