Jazz Jackrabbit 2 Plus (JJ2+) adds countless features and bug fixes to both Single Player and Multiplayer gameplay within JJ2, and is used almost universally by most serious players. It has much better network code than the original game, adding console commands to online games, fixing most major game-crashing errors and connection problems, allowing permitted clients to log in as "remote administrators" in someone else's server and control the gameplay, and adding several new multiplayer gamemodes. It additionally fixes or enhances many of the events in the game, and allows level designers far more power than in regular JJ2 through the addition of an easy-to-use scripting language. JJ2+ takes everything great about JJ2 and adds so much more on top of it; it is truly a must-download. JJ2+ is distributed under the MIT license.
Borrowing a name from the Unreal series, mutators will be new in JJ2+ v5.0 and can be thought of as miniature mods of their own. They're very similar in range to JJ2+'s existing scripting support, but instead of being tied to specific maps, online servers can enable or disable as many different mutators as they like in any map at all. A mutator shown here, for example, replaces JJ2's normal health system with a variant on the ring system from Sonic games.