Black paint

Black Paint is a toxic substance in Paper Mario: Color Splash. Throughout the events of the game, it possesses Bowser (turning him into Black Bowser) into stealing the Big Paint Stars of Port Prisma and ordering his minions to drain the island and its inhabitants of their color. Roy Koopa also used Black Paint in his battle against Mario and Huey, but it did not seem to impact his thoughts.

The substance is also supposedly painful to touch, as Mario took damage when he touched it in Sunglow Ridge. Also, Huey can supposedly get rid of large portions of the substance by himself in a short time, although how he does so is unknown.