StackMob 3.0 has now landed on SpigotMC, including many code improvements, performance enhancements and some (but big) features.
Added:

• MySQL support for caching entity data.
  
• Multiply-drops drops blacklist
• Player statistics support.
• Config auto-updater (finally) but it removes the comments - which is just how YAML is supposed to work.
• New API additions, the EntityStackEvent and a custom 'traits' system.

Fixed:

• After a zombie drowns, the drowned spawned does not have a stack value. (fixed for PaperSpigot users, a pull request is waiting for spigot.)
  
• TagTask and StackTask being CPU intensive. The StackTask has been split into tasks for every world. The TagTask has been split into another task for the 'show-player-nearby' feature.

'multiply-drops.whitelist' has been removed. it was pointless and the problem it tried to fix wasn't even fixed properly.