Right-Angle Sliding is a glitch in Mario's sliding behavior which occurs when Mario's facing angle and direction of travel during sliding are exactly at a right angle, which requires angle-perfect precision. Under normal circumstances, when sliding, Mario will turn to face his direction of travel such that his sliding angle and facing angle gradually converge. This does not occur when his facing angle is 90 degrees clockwise from his direction of travel, allowing the angle to be maintained indefinitely.
Right-Angle sliding occurs due to a mistake in the four inequalities governing Mario's turning during sliding. The difference between Mario's direction of travel and his facing angle is divided into four quadrants, and each inequality turns Mario in its own quadrant. However, the adjacent quadrants on Mario's right side both exclude a perfect right-angle, due to the use of greater-than expressions rather than greater-than-or-equal-to expressions. Because this angle fails all four inequalities, the code to change Mario's facing angle is effectively skipped.