The Black Triangles are the villains in the Symphony No. 5 segment in Fantasia 2000.
They are dark abstract shapes which resemble bats and are the nemeses of the Colorful Triangles. Given the fact that they emerge from the ground and try to take over the skies, they might be the an ancient, primordial force that existed before light (possibly either from the sun or the Force of Light in form of Colorful Beings) came into being. But once light began to shine the world and Colorful Triangles came into being, Black Triangles ultimately pushed back and locked inside the earth, further underground.
Resurgence and Demise
By the events of Symphony No. 5, when the clouds covering the entire world, Black Triangles used this opportunity to escape from their prison and attack the unsuspecting Colorful Triangles, killing many of them. They surrounded their surviving enemies and tries to deliver the final blow, but their nemeses uses rainbows to deflect them back.
When the hope seems lost, the sunlight suddenly shines through the cloud and shattered them.
Compared with Colorful Triangles, these Black Triangles are more chiropteran due to their black wings. They move in swarms both to attack their enemies, and to build seemingly impenetrable walls. Their only weakness is light, especially from the sun.