Bonded Construct can't attack alone.
6/22/2015 Bonded Construct can be declared as an attacker only if another creature is declared as an attacker at the same time.
6/22/2015 If you control more than one creature that can’t attack alone, they can attack together, even if no other creatures attack.
6/22/2015 Although Bonded Construct can’t attack alone, other attacking creatures don’t have to attack the same player or planeswalker. For example, Bonded Construct could attack an opponent and another creature could attack a planeswalker that opponent controls.
6/22/2015 If a creature that can’t attack alone also must attack if able, its controller must attack with it and another creature if able.
6/22/2015 In a Two-Headed Giant game (or in another format using the shared team turns option), Bonded Construct can attack with a creature controlled by your teammate, even if no other creatures you control attack.