This article is from the 2006 series of SMBZ and is no longer canon.
Shadow's primary transformation, Super Shadow, is much faster than normal Shadow and can fly indefinitely. His various Chaos powers also become enhanced, such as being able to throw Chaos Spears faster and charge them. Super Shadow is also invulnerable, although it is unknown if this invincibility would apply when fighting other super characters or characters of equal strength, such as Metallix.
Traditionally, Shadow needs the seven Chaos Emeralds to enter his super form, but in Super Mario Bros. Z, he can also use the power of the Star Spirits to transform. Sonic was seen transforming into Super Sonic by using a Starman, so Shadow may be able to as well.