These are custom blocks that you can place which disappear after placing. So you can get places without leaving a trail of blocks.



You can make a stack of temporary blocks by throwing an iron nugget with 4 sand.

There is more to it but for that check out the video demonstration



I made this on reddit a while back so I decided to set up a download link for it.



Video demonstration:-
www.reddit.com/r/MinecraftCommands/comments/hxlqwo/temporary_blocks_minecraft_datapack_updated/?utm_source=share&utm_medium=web2x&context=3