When Pia Nalaar enters, create a 1/1 colorless Thopter artifact creature token with flying.
{1}{R}: Target artifact creature gets +1/+0 until end of turn.
{1}, Sacrifice an artifact: Target creature can't block this turn.
Once a creature has blocked an attacking creature, activating Pia Nalaar's last ability won't cause the attacking creature to become unblocked.
20 Sept 2016
The “legend rule” cares about legendary permanents with the exact same English name. The Kaladesh™ card Pia Nalaar and the Magic Origins™ card Pia and Kiran Nalaar have different names, so you can control both at the same time.