See “Minion Lover” for a method to complete both achievements as well as for gathering a lot of gems.
Alternatively when you get all the tower heart pieces and you need to charge the heart in the wasteland Sanctuary, after the first charge it falls into a gnome village, use 5 blues to grab it which will reveal a Gnome hole underneath, out of which exploding gnomes will emerge. As soon as they start popping out, drop the heart and run for the water! The gnomes will continue to come out and die in the water, and give you a kill. You can also set a guard marker (hit ) right on top of the hole and your minions should take care of the gnomes, bring 5 or so back with you and use them to gather the lifeforce and gems that drop. Eventually the Gnomes will stop dropping items but they will infinitely spawn until you push the mother goddess statue over the hole. Be sure you are finished as after this you cannot remove the statue and no more will spawn.