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Beep Blocks (originally Beat Blocks) are a rare type of block found in Super Mario Galaxy 2, Super Mario 3D Land, Super Mario 3D World, and Captain Toad: Treasure Tracker. As their name implies, Beep Blocks are recognized for alternating between solid blocks and intangible outlines of various colours to the beat of in-game music. Because of this, Beep Blocks function as both platforms that Mario or Luigi safely can stand on when solid, or as deadly pitfalls in their "vanished" state. Depending on the game, both the physical appearance and functions of Beep Blocks differ.
Super Mario series
Beat Blocks are first seen in Super Mario Galaxy 2, appearing exclusively in the Beat Block Galaxy. In this appearance, all Beep Blocks are cube-shaped, and alternate between yellow and green. Mario or Luigi must traverse this galaxy, which is made up almost entirely of Beep Blocks, with caution and good timing. The player's Wii Remote will also beep three times before the Beep Blocks alternate. Due to the effects of the Double Time Comet, the Star mission "Silver Stars in Double Time" causes the Beep Blocks to alternate at four times their regular speed (despite the mission's name).
Beep Blocks return in Super Mario 3D Land, appearing in World 6-4, Special 3-5 and Special 7-2 (which is a revise of World 6-4, only with a Cosmic Clone chasing Mario or Luigi). In this appearance, Beep Blocks come in an assortment of shapes, and are now red, yellow and blue. In World 6-4 and Special 7-2, all three colors will appear one-by-one, then vanish in the same manner, leaving periods where all or none of the Beep Blocks will appear solid. However, in Special 3-5, the blocks alternate between one colour each time.
Beep Blocks return once again in Super Mario 3D World as they appeared in Super Mario Galaxy 2, but with their new name. They alternate between blue and pink-colored blocks. Later levels also include Beep Blocks in double time, as the game calls them, Blast Blocks. When they are in quadruple time, the frequency of alternating between different blocks is the same as the frequency of beat blocks' alternation under the orbit of the prankster comet in Super Mario Galaxy 2. Interestingly, Beep Blocks also appear in levels where the song has different beats per minute, but they still alternate in the beat of the original song's BPM (from Beep Block Skyway and Blast Block Skyway).
Captain Toad: Treasure Tracker
Beep Blocks appear in Captain Toad: Treasure Tracker. They behave mostly the same as in Super Mario 3D World and Super Mario Galaxy 2, but there is a longer period of time between the blocks switching. They are the focus of the stage Beep Block Sky Plaza.