Urza's Dark Cannonball

Shadow is an evasion ability.

A creature with shadow can’t be blocked by creatures without shadow, and a creature without shadow can’t be blocked by creatures with shadow. (See rule 509, “Declare Blockers Step.”)

Multiple instances of shadow on the same creature are redundant.

Exalted is a triggered ability. “Exalted” means “Whenever a creature you control attacks alone, that creature gets +1/+1 until end of turn.”

A creature “attacks alone” if it’s the only creature declared as an attacker in a given combat phase. See rule 506.5.