After you beat the Puff Beetle and obtain green minions then go to your dungeon.
Select Puff Beetle and get out as many of the green minions as you can control and have fun.
You get 75 green Lifeforce minus how many minions died. I usually lose about 5-10.
I am able to control 50 minions so it usually takes about 1-2 minutes. But for people who have 15 or less I would press Y near the entrance, to go back into the dungeon, and wait for your minions to be invisible, then get a few Beetles' attention and bring them back to your minions and so on.
I usually use them to upgrade my Steel and Durium Armor because I only use my Arcanium set
I also use them on my Arcanium Helmet because it doesn't matter which type of minions you use-they all give the same effect.