  A system in a quantum superposition of distinct states usually exhibits many
peculiar behaviors. Here we show that putting quasiparticles of graphene into
superpositions of states in the two valleys can complete change the properties
of the massless Dirac fermions. Due to the coexistence of both the quantum and
relativistic characteristics, the superposition states exhibit many oddball
behaviors in their chiral tunneling process. We further demonstrate that a
recently observed line defect in graphene could be used to generate such
superposition states. A possible experimental device to detect the novel
behaviors of the relativistic superposition states in graphene is proposed.
