The Armored Ventus Nightmare is the final boss of Kingdom Hearts 3D: Dream Drop Distance. It is a Dream Eater that has possessed Ventus's Keyblade Armor, which Ven had summoned earlier to protect Sora from the darkness.
The Armored Ventus Nightmare is essentially Sora, clad in Ventus's Keyblade Armor. The Armor bears a blackened color scheme and wields Sora's Keyblade, the Kingdom Key, in Ven's reverse-grip style.
Master Xehanort attempts to transform Sora into one of the thirteen Xehanorts and infuses his heart with darkness. While Ventus is able to shield Sora with his armor, the armor is quickly possessed by darkness.
With Sora unconscious, Riku is forced to dive into Sora's heart to save him. Upon arrival, the Nightmare emerges from the darkness and engages Riku in battle.
As the two fight, the Nightmare, as a last-ditch effort to defeat Riku, initiates a Shotlock, but Riku counters by activating Nightmare Clash with his Dream Eaters. Eventually, RIku is able to defeat the Nightmare and save Sora from within.