Andre sealed form (Dāku Andre) is Andre's darker form. His first appereance was in episode 40-41 when he sees Tifa injured and Babe is knocked out by Shinno. Andre uses his anger to achieve this state. While in this state, he shows his fury by destroying nearly killing Shinno. Story
Andre achieved this form by using his rage. He fights Shinno who wanted to test Andre's power at the time and nearly kills Shinno and takes a sadistic pleasure in doing so (indicated by his mad cackling and evil grin). Andre powers were shut down when he was calmed by Maki who says Andre normally acts much better than this.
Andre's sealed form looks similar to a normal wild Kitsune due to him growing pointy ears and a long tail except his body is taken over by the darkness with a black color, a dark blue aura, and his eyes become black while his pupils become yellow.