4 Oct 2004
The creature is destroyed if it does not attack because it simply can’t do so legally.
4 Oct 2004
It will require creatures with Haste to attack since they are able, but it won’t destroy them if they don’t for some reason.
1 Feb 2009
This will destroy creatures that weren’t able to attack because they had been previously tapped.
20 Sept 2013
If a turn has multiple combat phases, this spell can only be cast before the beginning of the Declare Attackers Step of the first combat phase in that turn.