The Familiar mod includes a little familiar for the player, so it's not always so lonely in SSP.
A Familiar is a kind of protector / companion that always follows the player.
They are not tameable like dogs and do not occur in the wild. These can be equipped like items / armor, Dungeon Defenders has inspired me.
The creatures do not only fly someone behind they also have a passive/active skill (attack by mobs, heal the player etc).
Some are not available from the beginning, you need to unlock them first (buy with XP or unlock achievements).
Includes Extended, DefaultMobs & Herobrine FamPacks.