This mod enables users with permission ninja.basic to be invisible to all other users of the server, when sneaking (default shift).
It is designed to prevent invisible players from killing others relentlessly/outside of the victim's power. Because of this, you cannot be invisible when flying or in the air. (I feel as though the in-the-air part contributes to the ninja element)
This makes killing people without them seeing you and being able to defend themselves impossible because you have to move very slowly, cannot jump, and cannot fly speedily around them.
Commands
/ninja enables the ability
/normal disables the ability (you can sneak like normal)
Changelog
1.0 - basic permissions and commands
1.1 Removed logs, fixed bugs, updated to 1.3.1-R1
1.2 Added config file, defaults to OPs being able to see invisible players
Fixed errors that were being printed to the log.
Updated to 1.3.1-R2
1.3 Added smoke-bomb type effect. Whenever you first go invisible, a ball of smoke appears around you to everyone on the server including yourself. Looks like/has this effect.
Added particle effect that only appears to yourself when sneaking in ninja mode. Lets you know that you are invisible.
Fixed errors that were being printed to the log again.
1.4 Updated to 1.4.2 R0.3
Fixed errors being printed to log.
Open sourced it!
1.5 Update to 1.4.6 R2
Made some of the code more efficient to reduce lag
Video
Source
View and fork the source here.

