"Action Shot" is an achievement that requires you to take a photo with 5 subjects in it (hostiles or friendlies). You can try to do it by gathering several enemies and having some enchanted armor of your own but in this guide, I will teach you how to assemble such a formidable army that you won't even need to put yourself in harm's way.

• Chapter 3 : Edgar
  He can be found in the Strange Bedroom, accessible from the Hallway next to the Infirmary. Before you can recruit him, you will need to speak with the king in the Throne Room (don't forget to wear the nurse outfit). Edgar is not allowed to leave the house so keep that in mind.
  
• Chapter 3 : Horace
  You will need to reach the Cagewood circus. If you already know where this is, skip to the next paragraph. You first need to complete the first mission for the king (the one where he asks you to deal with the witch from the basement). This will allow you to leave the house from the right, where a bossfight awaits you. After defeating the boss you will reach a crossroad where you see the Lord of Nowhere. If you were to keep walking right you would reach the church, take the crossroad instead then keep walking right until you reach a ferryman. Buy his boat pass then ask him to "Go west" then keep walking west until you find a clown NPC.
  
  
  Buy the entry fee to the circus and find the prize seller.
  
  One of the prizes is a Dog Whistle. Buy it and you will have a recruitable dog companion waiting for you in Nowhere.
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  He will go back there whenever he dies. You even keep him in NG+ when you reach chapter 3 again.
  
  
  
  
  
  
  
  
  
  
  
• New Game Plus only : Nightingale's creature
  Once in NG+, go to the West Basement Stairwell and speak to the figure in the wall. She will ask for a Starry Flesh. You can get those from the new Angel ennemies, exclusive to NG+. One of them can be found where the Vicar used to be in normal game, at the right exit of the house.
  
  She will get you to Central Nowhere and give you a mission: collect even more Starry Flesh. The doll NPC can exchange Organ Grease for Starry Flesh. The items you buy with Starry Flesh in the "Prizes" shop count towards the mission.
  
  Once you have completed your mission, kill the secret final boss and Millie will tell you an area was opened in the Church of Burdens. The Church of Burdens can be accessed by going downstairs through a door in Central Nowhere.
  
  Go there and talk to the NPCs and they will explain to you how to summon the creature. For that you will need to carry the Book of Burdens, that you can pick up from the statue in the previous room. It's essentially hard mode as long as you have, it just needs to be in your inventory. For every new enemy you kill while carrying it (including bosses), you get Dream Essence (you will know it worked if you get a bestiary entry with inverted color).
  
  Dream Essence is used at the Church of Burdens to unlock Nightingale's creature and then to strengthen it even more.
  Note about the creature : The darkened pages stay dark in subsequent NG + cycles and you don't get more Dream Essence in the next NG+ cycle if the page was already darkened, meaning that there is a cap to the creature's level and you can kill the enemies you missed out on the next cycles if you wish to do so.
  Also, with a full darkened bestiary, you are left with 3 Dream Essences. This is normal and as of yet we don't know of a way to use those.

Once you have gathered your companions, you can complete their numbers with some enchanted statues (use the Enchant spell to animate them). You can usually find some on the first floor of Mostyn House, in the Upper Banquet Hall and the Upper Balcony.
Just have them stack, take a few steps back, take the photo and voilà, you get the "Action Shot" achievement.

I didn’t test if you could include friendly NPCs for the achievement to count (for exemple the ones from the Throne Room). I cannot test anymore since I got the achievement but if you manage to do so, please say so in the comments.