What it does
Stuck on the "Loading terrain…" screen. Looks like the world is still loading.

How to turn off
Run the command again on the same player.

After rejoin
Goes away when they leave the server.

What it does
Shows the demo screen on their screen and they can't close it (only operators can close it without problem).

How to turn off
Run the command again, or use /demoscreen off <player>.

After rejoin
Stays on until you turn it off.

What it does
Plays the end credits on their screen.

How long
Happens once when you run it.

Note
They can leave it the same way as on the normal end credits screen.

What it does
Makes them download and use a resource pack from a link you send (must start with http:// or https://).

How to turn off
Use /resourcepack <player> off.

What it does
Kicks them with a fake error message. Looks like their internet or the connection broke, not a normal server kick.

How long
Instant. Happens once when you run it.

What it does
Sends them to another server.

Example
play.example.com or play.example.com:25565

What it does
Opens their inventory in a chest screen so you can look at and change their items.

How long
Only while that screen is open.

What it does
Hide from other players. You can fly and you won't take damage.

How to turn off
Run /vanish or /v again.

After rejoin
Stays on until you turn it off.

What it does
When you die, others see you dying and get the normal death message. But you switch into vanish and stay at that position.

Watch out
You still lose your items if keepInventory is off.

How to turn off
Run /deathvanish again before you die.

What it does
Sends a fake "left the game" message in chat and hides you from the player list.

How to turn off
Use /fakejoin.

What it does
Undoes /fakeleave and sends a fake "joined the game" message.

Shows all commands in chat.