Hey,
I created the gamemode "One in the chamber" in Vanilla Minecraft with just functions!
Normal rules: https://hivemc.com/one-in-the-chamber
The only difference to my version:
You can die as often as you do, the first player with 5 kills wins the game.

To play, just upload the map on your server and type this command:
/function oitc:setup
Done!
You also can build your own map at the position the preset map is positioned! (So its basically a sandbox)

To use it in your own world, here's the download link for the import:
http://www.mediafire.com/file/oaf3co686og757r/OITC%20functions.zip
Once you have downloaded th zip file, extract it into any folder, run the .bat file and follow the instructions. Then join your map, type /function oitc:setup, place the spawn eggs:
spawn - where the server spawn point should be
start - where the noteblock to start the game should be placed
mapmitte - in the middle of your oitc map (30x30 blocks)
invisibleCounter - place it near the spawn
reset - if at the scoreboard on the right there is a number higher then 1 place this egg. then you have the other spawn eggs to place again.

if on the scoreboard everything is set to 1, click the carrot on a stick and your map is ready to play!


Changelog:
01/10/2018: v1.0: Command Mod release
01/09/2018: v1.0: Map release

What I will definetly do:
+function pack (to add the "mechanics" to your own map or to a downloaded map)
+range of gamemodes (for example "Last man standing" or "10 kills = win")

What I maybe will do:
-update the whole thing to 1.13
-"convert" the map to a 1.13 datapack so you can add it to your existing datapacks (for example ranks)