Just something i would love to see :3 would be nice to have some newer mobs come in and replace maybe some old ones you know?
The only mobs that aren't in game atm are the Illager mobs, Vex, and Parrot. Would be nice to have them though, but it might be better to wait for 1.13 when an influx of new mobs will be introduced.
Currently we are improving the documentation of MassiveMobs, mainly for internal staff use and improved creation in the future. New MassiveMobs is tedious but is something that’s has been discussed within staff and while I can’t make promises of new mobs, it’s definetly something that’s we will be looking at in the coming weeks and months.
What cnoc said, MassiveMobs is getting a rework on the admin side of things, but we've got some passionate people on the team (cough Kaezir cough) who want more mobs and more unique mobs on the server.
MassiveMobs has since been removed from the server and currently there are no plans to bring it back. If we do, however, it would take quite some time for us to rework mobs and ensure they don't wreak havoc in terms of lag.