2014-02-01 : Impetuous Sunchaser attacks only if it’s able to do so as the declare attackers step begins. If, at that time, it’s tapped or affected by a spell or ability that says it can’t attack, then it doesn’t attack. If there’s a cost associated with having it attack, you’re not forced to pay that cost. If that cost isn’t paid, Impetuous Sunchaser won’t attack.

2014-02-01 : You choose which player or planeswalker Impetuous Sunchaser attacks.