BungeeCord, the 6th in a generation of server portal suites. Efficiently proxies and maintains connections and transport between multiple Minecraft servers.
Let Player1 join using Minecraft 1.6.4 and Player2 using Minecraft 1.7.4
/scoreboard teams add test
/scoreboard teams option seefriendlyinvisibles true
/scoreboard teams join Player1
/scoreboard teams join Player2
/give Player1 373 1 14
/give Player2 373 1 14
Now Player1 and Player2 drinks the invisible potions and you'll see that Player1 see Player2 like a ghost but Player2 doen't see Player1
If you create a scoreboard team with seefriendlyinvisibles enabled you can invisible friends in 1.6.4 but not in 1.7.2 and 1.7.4.
My server is spigot 1.6.4 R1.1 and proxy server is updated to https://github.com/TheUnnamedDude/BungeeCord/commit/64a8182de9c7a95eab340e47f1eec18e5d04c641
You can reproduce it with scoreboard commands:
Let Player1 join using Minecraft 1.6.4 and Player2 using Minecraft 1.7.4 /scoreboard teams add test /scoreboard teams option seefriendlyinvisibles true /scoreboard teams join Player1 /scoreboard teams join Player2 /give Player1 373 1 14 /give Player2 373 1 14 Now Player1 and Player2 drinks the invisible potions and you'll see that Player1 see Player2 like a ghost but Player2 doen't see Player1