Minecraft – How to teleport players in half-block increments

This is actually not too difficult to implement by using scoreboard magic.

First, set up some scoreboard commands

scoreboard objectives add airborne dummy
scoreboard objectives add fallen dummy

Next, run the following commands on a fast clock (I suggest using a fill clock), in this order.

scoreboard players set @a airborne 0
execute @a ~ ~ ~ detect ~ ~-1 ~ minecraft:air -1 scoreboard players set @p airborne 1
scoreboard players set @a[score_airborne=0] fallen 0
scoreboard players add @a[score_airborne_min=1] fallen 1

The first two will set airborne to 1 for every player who is not standing on something, i.e. the block beneath him is air. The third command will reset the fallen score to 0 for everyone who is not airborne, the fourth increments the score 20 times a second instead. This means that fallen is 0 as long as you were standing on something since your last fall.

Now you can select the falling players for teleportation using @a[score_fallen_min=XYZ]. Replace XYZ with however many seconds a player has to be above air to be considered "falling", multiplied by 20.

There is an issue with this however: Standing on the edge of a block will make you be considered falling, and I can't think of an elegant solution to this, short of chaining execute detect commands to check a 3×3 area below the player for blocks.

Use pairs of one Repeat and one Chain Command block, one pair for each type of block (or for smaller numbers use good ol' Redstone clocks).

The repeat command block will test if there is a specific block one block under the Player:

/execute @e ~ ~ ~ testforblock ~ ~-1 ~ minecraft:YOUR-BLOCK-ID

And the chain one will add one to your scoreboard:

/scoreboard players add @a YOUR-BLOCK-ID 1

Note:
First you want to create the objective(s) and make them visible:

/scoreboard objectives add YOUR-BLOCK-ID dummy

/scoreboard objectives setdisplay sidebar YOUR-BLOCK-ID

And you want to create one objective for each block you step on frequently: grass, dirt, stone, cobble, wood logs, stairs, slabs and planks, netherrack, farmland, gravel, sand, air, water, …

Example:

First, create the objective:

/scoreboard objectives add dirt dummy

And make it visible:

/scoreboard objectives setdisplay sidebar dirt

Then, in a repeat command block, put this command:

/execute @a ~ ~ ~ testforblock ~ ~-1 ~ minecraft:dirt

And if it returnes true, execute this command:

/scoreboard players add @a dirt 1

Now, for each tick you step ( = are above) on one of the blocks you chose to put into your system, it's score on the left of your screen goes up. The blocks with the highest scores go up in the sidebar list.

You can also use good old comparators and redstone clocks to avoid numbers like Dirt: 8294, Grass: 34890