Struggle Bats are the primary weapon of Twilight Town's Struggle competition during both Roxas's and Sora's story of Kingdom Hearts II and Kingdom Hearts II Final Mix. The Struggle Bat is also used by Roxas in Kingdom Hearts 358/2 Days for Mission 37, while playing Grandstander. They also act as a basic means of self-defense for Twilight Town's residents, as demonstrated when Seifer utilizes one for this purpose.
In the Simulated Twilight Town before Roxas's first Struggle battle, Roxas must select which Struggle Bat he will use in the following rounds. Picking your Struggle weapon (staff, sword, etc.) is a call-back to choosing between Dream Sword, Dream Rod, and Dream Shield in the Awakening sequence in the original Kingdom Hearts; unlike Kingdom Hearts, however, the Struggle Bat only gives a bonus to a particular stat and will not dictate the order Sora will learn his abilities in.
The Struggle Sword is the most commonly used bat; all of the characters you fight against in Struggle will use this bat. It is simple in design - having only a straight golden handle that curves to a 90° angle at the pommel, and a thick blue "blade" extending from the thin "guard," that barely extends past the diameter of the blade.
This bat is for those who favor strength in battle, giving a +1 STR bonus when chosen, and is easier to use in fast, powerful strikes.
The Struggle Hammer is one of the two Struggle bats that only Roxas can use. The "blade" is similar to that of the sword, but the handle is thinner, and there is a wide, moon-shaped hand guard that wraps from the hilt around the hand, similar to a rapier. This bat also has a thick and slightly more ornate pommel.
This bat is designed for finesse and defense. It gives a +1 DEF boost when chosen, and is best for guarding against attacks.
The Struggle Wand is the other Struggle bat that only Roxas can use. This bat is quite different from the other two in that, rather than having a short gold handle and a long blue "blade" used for fighting, the staff has a long handle, tipped with a blue star that acts as the weapon.
This bat is made to accommodate magical abilities. When chosen, it gives a +1 MAG boost to Roxas. It provides balance for good finishing moves and powered attacks. It is unknown if this bat has any magical abilities, but it seems to be more in the ways of Donald's staves and magic wands. This, along with the Yen Sid-like star motif, makes it a likely candidate for channeling magic.
It's no use...
Roxas, using a struggle bat to fight the Nobodies in Twilight Town
While the material composing the Struggle Bats is not confirmed, it is highly likely that they are made out of a blue NERF-like foam, due to their use in a children's game. The handle is sturdy and golden in color, and also of an unconfirmed substance. Whatever they are in fact made of, Struggle Bats are completely ineffective against Nobodies.