Java Edition:Floating Gravity Block
Gravity effected blocks are blocks that require a block to stand on, otherwise, they'll become entities and fall until they hit a solid block. Some bugs allow a gravity block to float without the need of any supporting blocks.
Obtaining
Classic
In c0.0.15a - c0.0.23a_01, making sand or gravel fall onto water or lava places the block on top of the water or lava. You can also make sand or gravel float in the air by drying up the water with a sponge due to it not updating the sand.
Signs
By letting a gravity block fall on top of a sign, it'll keep bouncing on top of it. Placing another gravity block on top of the bouncing block and reloading the world will cause the top gravity block to remain suspended. This works from version Infdev 20100618 to Infdev 20100630-2.
This method is not consistent, and may have to be attempted multiple times.
Floating Point Error
For every other block from 2^23 blocks out to the world border, if you place a gravity block the block will not fall. This works from Infdev 20100618 to 14w31a (1.8 snapshot).
Generation
Sand, gravel, and red sand all generate naturally in the world. When a cave, ravine, lake, or even just a cliff turns the block underneath them to air they will not automatically fall. This bug is however limited to where these blocks generate, no way to get it in other areas of the world. It's also the only intended method of obtaining floating gravity blocks.[1]
Update Suppression
Using update suppression, the player can remove the block underneath any gravity block and it will not update the block. This works from Beta 1.6 Test Build 3 to 1.21 (present).
Tall Flowers
By placing a gravity block on top of a tall flower and breaking the base of the flower, the gravity block will remain suspended.[2] This works from version 13w36a to 1.13-pre2.
After 1.13-pre2, tall flowers are treated as blocks that gravity blocks can fall through, so just updating gravity block on top of a tall flower will make it float.
No Update Piston Retraction
By placing a gravity block on top of the extended arm of a sticky piston attached to a slime block that has reached push limit, then retracting the piston arm the gravity block will remain suspended until updated.[3] This will also suspend any item that requires a block to stand on and can be placed on top of an extended piston arm, such as water, lava, sea pickles, carpets, banners and signs, but not lanterns and bells. Works from 17w49a until 1.21 (present).