Ghost Block... NOW WITH COMMAND BLOCKS!

1. Place a repeating command block with the command: summon minecraft:falling_block ~ ~2 ~ {"Motion":[0.0d,1.0d,0.0d],"Time":1} (the type of falling block may also vary).

2. Place a lever next to it, flick it, wait a bit (4 seconds is enough) and flick the lever again.

3. You get a ghost block.

Behaviour:

1. Acts like air (cannot be broken; doesn't highlight; sand above it displays particles, but doesn't fall down on update, if it's sand).

2. It "teleports" the player back (if attempted to go through).

3. Slows down the player if attempted to walk on (like soul sand, but much slower).

4. Items, thrown on it, jump up and down (much like #MC-4).

5. Water and lava (but not blocks) cannot be placed through/inside it and instead places in front of it.

6. Blocks water and lava.

7. Transforms anything placed instead of it into its type (not glitched anymore).

8. When the block below breaks, becomes normal falling block (if it can fall) and doesn't glitch out anymore.