Heroes of the Third Sphere

When Heroes of the Third Sphere enters the battlefield or attacks, if you control no other
Knights, create a 3/2 red and white Knight
creature token with "When this creature attacks,
if you control no other Knights, return a card
named Heroes of the Third Sphere from your graveyard to the battlefield," and "{r}: Target
creature with power 2 or less can't block this turn."
{2}{w}: Attacking creatures you control get +1/+0
until end of turn.