Eater's Bone

Nearly every pet in the game teleports to you once you outrun it. This one does not. The baby eater flies after you under its own power, which means it falls behind on any long horizontal sprint or fast drop and turns up again minutes later. Some people like that, since it reads as an actual creature rather than a sprite stapled to your shoulder. If you want a pet that stays on screen, pick a different one.

For a stretch of early versions this effectively did not exist. A bug had the Eater of Worlds handing out an asphalt crafting station in its place, so anyone killing the boss for a pet walked away with a machine instead. It took two patches to sort out properly.