Historical Rules · 11 November 2016
Rule 702.115a
Official source text from the 11 November 2016 Rules release
Myriad is a triggered ability that may also create a delayed triggered ability. “Myriad” means “Whenever this creature attacks, for each opponent other than defending player, you may create a token that’s a copy of this creature that’s tapped and attacking that player or a planeswalker he or she controls. If one or more tokens are created this way, exile the tokens at end of combat.”