How do I become the Puppet Master?
Big Bad Voodoo doesn't really count as a pet,it is more like AOE ward.
On lvl 30 you will get fetish army and it makes an easy achievement.
Also additional followers you get from quests like Tyrael,Leah... don't count.But main followers templar,enchantress and scoundrel do.
The fetish army is your best bet. I'm fairly certain the Big Bad Voodoo fetish doesn't count, but the six dagger wielding fetishes plus your zombie dogs and gargantuan will get the achievement.
That's how I got it.