I like the pets currently as they are, but I would like to see a little more variety. I also love the way rangers get their pets. I’m think it would be cool to have a system put in similar to the rangers for Necros. Come across certain types of undead, give the necro the ability to enslave them and pick them from a list. to use in place of one of the current pets. More or less a skin as they could have the same ability as the current pets. Make the list that you can choose from in your pet browser be segregated by what pet it would replace in your abilities.
For example. You have unlocked flesh golem and come across a skeletal knight you like the look of. You enslave the knight and then look him up in your pet browser and see that your skeletal knight can replace your flesh golem in appearance. All of the skills for the flesh golem are still there, you just have a better looking or more unique skin for him. It’s more about personal customization than stats that way and nothing falls out of balance.