Whenever you play a land from exile or cast a spell from exile, create a 1/1 colorless Thopter artifact creature token with flying.
Pia Nalaar turns impulsive exile-and-play effects into a steady stream of hasty flying Thopters. You set up cheap impulse-draw and exile engines, cast everything off the top of your library to flood the board with attackers, then overrun with anthems or sacrifice the swarm for value. The deck wins through repeated incremental advantage and a wide, evasive army.
Generates evasive flying tokens for free off cards you were already going to cast
Built-in haste makes every Thopter immediately relevant for offense or blocking
Cheap two-mana commander that snowballs quickly and is easy to recast
Synergizes with Boros's deep pool of impulse-draw effects that are otherwise underused
Token swarm plays well with anthems, sacrifice, and artifact payoffs