Found something wrong? Let us know at the forums!
Mobs is a plug-in that is available for free. You can find and enable Mobs in the Optional Features list of the app. By default this setting is disabled because it might lag your server due to increased workload. If you feel like your server is lagging while using Mobs then try disabling it.
When this plug-in is enabled, all kinds of neutral and aggressive mobs will be able to spawn in your server, such as cows and zombies.
Have a question about the plug-in Mobs? Ask it on the forums here!