When I add it, the entity wont spawn...
Also, something I didn't mention, the mob moves really laggy when hit (the 'jumping' and falling).
Does anybody have an idea how to fix this?
Make sure the player isn't null... Where are you setting the player?
Also, instead of showing snippets from your code, try a git repo... It's better because we don't have to ask for code everytime.
I think he was trying to say that there is a plugin which has the command /rewards that opens a gui which he calls by doing mc.thePlayer.sendChatMessage("/rewards");
That's because you have
Which requires you to the color code in your lang file, remove it.
To make it have colors you put § + a number in front of the 'translation'.