Psychic Sword

Equipped creature gets +1/+1 and has "When
this creature attacks a defending player with a
higher life total than equipped creature's
controller, it gains +X/+X until end of turn,
where X is the difference in creatures
controller's life total and defending players life
total."
Equip {4} ({4}: Attach to target creature you
control. Equip only as a sorcery.)