User blog comment:Tachikaze Master/So I noticed something.../@comment-11372432-20150407090335/@comment-24965906-20150407131226

It depends on when Sleipnir is called.

If the attack was declared, and then you decide to call Sleipnir, you still get hit, because the attack was not redirected.

If you decide to call Sleipnir before the attack was declared, or immediately after a previous attack had hit, then you opponent has to attack Sleipnir.

BONUS: If your opponent attacks a monster in your centre, and you call Sleipnir over that monster, then the attack is said to have missed, and nothing happens.