2017-03-14 : If the target creature is an illegal target when Fists of Ironwood tries to resolve, Fists of Ironwood won’t resolve and won’t enter the battlefield. You won’t create Saproling tokens.

2017-03-14 : The Saproling tokens aren’t created until after Fists of Ironwood is on the battlefield, so you can’t cast Fists of Ironwood on one of those tokens.

2017-03-14 : You create the Saproling tokens, even if Fists of Ironwood enters the battlefield attached to another player’s creature.