The second video in this thread is slower and more comprehensive.
The third video in this thread is higher quality.
List of Basic UHC Commands
Health Regen Off
/gamerule naturalRegeneration false
Set World Spawn
If you want zero zero to be spawn, you can set it with this command. If you are using command blocks instead of chat commands, the command blocks will need to be in the same chunk as spawn so they continue to operate even when players are not around.
/setworldspawn X Y Z (use any coordinate)
/setworldspawn 0.0 0.0 0.0
World Border Set and Add and Subtract value
/worldborder center X Z Use the coordinates for the center of your map or spawnpoint. You don't need the Y coordinate.
/worldborder set 2000
/worldborder add 500
/worldborder add -500
Create Teams [These team commands are pre 1.12]
/scoreboard teams add blue
/scoreboard teams add red
Assign Random Players to Teams [These team commands are pre 1.12]
/scoreboard teams join blue @r[team=,c=3]
/scoreboard teams join red @r[team=,c=3]
(the last value, here a "3", is the amount of players to be put on that team)
(if you want to assign players to specific teams, just put their name after the color. You can do this in chat)
Color the Names in the Sidebar blue or red to Display Teams [These team commands are pre 1.12]
/scoreboard teams option blue color blue
/scoreboard teams option red color red
Clear Teams for Reset
/scoreboard teams remove red
/scoreboard teams remove blue
/spreadplayers X Y <value for how far apart the players will be> <value for how far players will be from center> <true or false (true for teams) @a
The X Y is the location where the players will be spread from, followed by far apart value, followed by distance from center.
/spreadplayers 0.0 0.0 100 500 false @a
Show Hearts in the Tab
/scoreboard objectives add Hearts health
/scoreboard objectives setdisplay list Hearts
(After the commands are entered, the hearts will not show up in the tab until you take some damage.)
If you want to customize your UHC, try out these scoreboard commands
Add Gold Ingot Objective to Scoreboard
/scoreboard objectives add gold_ingots dummy
Scan Inventory for gold ingots: 4 Command BlocK
Tracking gold_ingots is not a default scoreboard objective; you will need these four commands in command blocks running in a circuit for continuous scanning to update the scores.
Just to save you some time. The 1.13 all-in-one does not really work in 1.14. You might be able to get it to work by using a command block in a minecart on an activated rail, but it's pretty unreliable.
I have already done some UHC with my friends thanks to this "all in one command", now we would like to solve the problem about the commands not working on versions like 1.14 and 1.15 cause it could be cool to play UHC on the recent versions