Board Thread:Questions and Answers/@comment-28050300-20160325013221/@comment-11005605-20160325053505

Yes you can. As long as you can pay the Cost, you can play the Boot ability of a Z/X during your Main Phase or both Players' attack. (Well except when the opponent has Flonne up.) That said, you cannot play Boot abilities with a Sleep Cost because you would be unable to pay the Cost if your Z/X is already in Sleep.