The Twilight Thorn is a boss from Kingdom Hearts II.
The Twilight Thorn is a giant Nobody that attacks with lightning-like thorns, and shares properties with other deformed Nobodies: it can stretch and contort its body and possesses remarkable maneuverability.
Only one appears, in Kingdom Hearts II, when Roxas goes to the Station of Awakening. It is interesting to note that when Roxas senses a presence and turns around to see who it is, he sees a person wearing an Organization cloak, just before it turns into the Twilight Thorn. It would make sense that the figure is Roxas, just as Sora turned around to see his shadow become Darkside Heartless.
The Twilight Thorn battle shares many notable similarities with Darkside, a gigantic humanoid Heartless. Both prominently appear in Roxas and Sora's awakenings, respectively, and are the first bosses of the game. They also seem to share close connections with Roxas and Sora (again, respectively): the Twilight Thorn appears as Roxas' former self, while Darkside is born from Sora's shadow. The two are also both able to summon lesser Heartless/Nobodies to attack. They are both fought in the same area, Dive to the Heart. As the Twilight Thorn dies, darkness spews from its body and nearly consumes Roxas, reminiscent of how Sora was nearly consumed by darkness that erupted from the first Darkside in his own awakening.
At the same time, the two creatures share key differences, being a Nobody and a Heartless. Darkside has wild, unkempt tendrils that covers its face save for two yellow eyes, while the Twilight Thorn has wild blue scarves around its neck, and lacks a face of its own.
Note: The Twilight Thorn is not registered in Jiminy's journal until you enter the Simulated Twilight Town. This is strange because Sora doesn't meet the Twilight Thorn. However, this may be Roxas's memory of his own Awakening instead. Twilight Thorn may be the Nobody of a person that turns into a Darkside Heartless.
Journal Entry
A giant Nobody who Roxas fought at the Station of Awakening.
Although it tried to capture Roxas with its thorns, it was overpowered and defeated by the strength of the Keyblade master.