Splotchy goop

Splotchy goop is a type of black goop that appears in the Bowser's Fury mode of Super Mario 3D World + Bowser's Fury. Splotchy goop can be found polluting the waters of Lake Lapcat, and it is present due to Fury Bowser, whom Bowser Jr. covered with the same goop, transforming Bowser into his Fury Bowser form. Sometimes, when the player finds Cat Shines, some splotchy goop in areas near the site of the Cat Shine disappears, usually revealing a new Cat Shine. However, Lake Lapcat cannot be completely cleansed of splotchy goop.

Attempting to swim in this goop results in Mario taking damage; this is unavoidable, as it negates the effects of all power-ups, including the Super Star and Invincibility Bell. If Plessie swims into the goop, he dives below the water and resurfaces in an area without goop, leaving Mario to take damage. Small areas of goop can be traversed by utilizing the short invincibility granted after Mario takes damage. If he attempts to leave the borders of the in-game map, an invisible border prevents him from progressing. This border is also present around Fur Step Island before Giant Bowser is defeated at least once to prevent the player from re-accessing the area.