This addition would add certain mobs players can give names to that would follow them around the server, it would be fun to explore and go on adventures with your little friend :D. Pets would also be an incentive to get players donating to help keep up the server, higher ranks could get access to more and more mobs as pets for example: VIP has slime as their option for a pet, Premium could use slime and a chicken, adding more and more options each rank, obviously you wouldn't add anything crazy like enderdragon or wither. llamas would be nice though :)
In summary I don't believe this plugin would add extra lag if incorporated correctly (not adding enderdragon, wither...), it would be a great incentive for donating for ranks to help keep up backups and help things run lag free :) (This is how it would benefit the server), most importantly it would just be neat to have and fun :).
