Players can't cast spells during combat.
: Target creature attacks this turn if able.
9/22/2011 While Basandra, Battle Seraph is on the battlefield, players can’t cast any spells during the combat phase, including permanent spells with flash.
9/22/2011 Players may still activate abilities during combat.
9/22/2011 If, during a player’s declare attackers step, a creature is tapped, is affected by a spell or ability that says it can’t attack, or hasn’t been under that player’s control continuously since the turn began (and doesn’t have haste), then it doesn’t attack. If there’s a cost associated with having a creature attack, the player isn’t forced to pay that cost, so it doesn’t have to attack in that case either.