Um, I forget how the ability works, and I'm too lazy to search through two pages of old posts. However, shouldn't the wording be "For Stealth Flier's next attack..." instead of "When Stealth Flier attacks..."?
The way it's worded, one would assume it's a one-time-use ability, like Lycanthrope, that does all that good stuff if it attacks and there is at least one empty creature space on your side of the field. This would result in Stealth Flier moving to a creature space that has not been activated yet, making it so that Stealth Flier to attack when the creature space is eventually activated, which means Stealth Flier can attack 23 times per turn.
