So i see that SDK's gun mod can be used on multiplayer if there's server mod and client mod, however when i looked in craftbukkit.jar i can't see the things like minecraft-server.jar however i want to implement the SDK's gun mod into multiplayer while i can use bukkits' plugins... Is there any way that i can implement SDK's gun mod into craftbukkit.jar? (I tried the way to implement it into minecraft-server.jar into bukkit.jar, this is what happened. java.lang.NoClassDefFoundError: kh at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClassCond(Unknown Source) at java.lang.ClassLoader.defineClass(Unknown Source) at java.security.SecureClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.defineClass(Unknown Source) at java.net.URLClassLoader.access$000(Unknown Source) at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at org.bukkit.craftbukkit.Main.main(Main.java:83) Caused by: java.lang.ClassNotFoundException: kh at java.net.URLClassLoader$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) at java.lang.ClassLoader.loadClass(Unknown Source) ... 13 more ) Thanks to whoever watched this post! And millions thanks to one who helps me to fix! (Bad English Sorry..)