Ideally this is done by unlocking the Pack-a-Punch machine by completing the 4 rituals around the map. (One for each character) I have also added a video guide on how to do this. It can be found at the bottom of the guide,NOTE:
Every second ritual (so 2 and 4) a Margwa will spawn after you pick up the Gateworm. You have to shoot the head with the mouth open (yellow light) to kill it.
To start you want to get the Golden Fountain Pen by opening up the gate, then transforming into The Beast and hitting the glowing red box on the back of the truck to open the summoning key, then running forward and shocking the electrical box (LT) on the crane. This will cause the crane to drop the pen. To save time and beast modes, turn around and look up. You will see a glowing red eagle head and a grappling hook icon will appear over it. RT will grapple you to it, and then sprint up the stairs, through the room, and out towards the outer stairs where there is another electrical box to shock with LT that will open the gate and extend the stairs. This opens up the first ritual room. You should then be out of time and returning to human.
From here kill all but one or two zombies, and head up the newly opened stairs. Walk up to the altar and hold X once, and then X again to place the pen and the summoning key on the altar. This will begin the ritual, and you then need to walk calmly around the room in a big circle. You should only need to sprint if a Keeper gets close to you, but a walking pace will keep them all behind you. Once a white light flashes the ritual is done and you can go collect the gate worm.
Now you get to choose your own adventure. Choose one of the three gates in the Junction area to open.
Waterfront Station: This is the gate directly to the right of the spawn alley. As soon as you open the gate you will see a purple Beast curse site. Become the beast, and turn to the right and you will see a gated stairwell like the first one you unlocked. The electrical box is at the top on the right wall and you can shock it from the ground where you are if you are right up against the gate. Once you shock it run down the alley (not up the stairs) and if you look up you will see another glowing eagle head with a grapple symbol. RT up to it and turn around. You will see another eagle head. RT again and move forward to melee the glowing red box to the ground. From here jump up and over the railing to land on beyond the next gate you have to pay to open, and keep running down to the docks. Once there turn left and melee the door open. This is the second ritual room.
Pick up the Championship belt you knocked down with the box and open the gate to the docks. Zombies permitting, begin the ritual and once again walk around the edge of the room. I prefer to go up the stairs into the office when I do it, but it can be done just around the boxing ring as well. White light flashes, acquire your new gate worm.
Canal District: Once you open the gate here, the Beast curse location is to your right. Use it and run into the district under the first archway. Look up and to your left and you will see an eagle head. Grapple up and turn a 180 to run across the bridge and through the room to shock the box to unlock the stairs. After that jump into the canal and you will see a large glowing door on your right. Melee the door, and the small grate to the right of the door. Run forward and you will see a glowing portal on your left with an electrical box. Shock the box and beast mode should run out. Drop into the canal and retrieve the Police badge from the small grate next to the door.
Now you will need to open the second gate in the canal district which opens access to the Ruby Rabbit which is the next Ritual site. Beast mode and look up at the Ruby Rabbit roof area. You will see an eagle head there. RT up and run inside. Drop down a level, then go down the stairs. There will be an electrical box to shock that will activate the stairs to the Ruby Rabbit. Run up the stairs and begin the ritual with the normal walking pace you are now accustomed to. You now have 3 precious bundles of joy.
Footlight District: The beginning of this area is very similar to the Waterfront Station. Enter beast mode and look to the right where a stair gate is located. Again you can shock the box from the ground level. This time run up the stairs and turn the corner. You will see a ramp leading off of the edge. Sprint toward it and jump across the gap to the other side. There will be a glowing red box you can melee. You can then exit beast mode and drop down to retrieve the hair piece.
Now you need to open the second gate to the main square area. There will of course be a Beast site here as well. Activate it and look up to the large Burlesque building. At the top will be an eagles head to grapple on. This will then cause you to fall a bit, and when you turn around you will see an electrical box on the back of the main sign. Shock it and the burlesque will now be open for the final ritual. Start the ritual, walk walk walk RUN! walk walk walk. Congratulations.
Now you will need to head back to the canals district or the Waterfront station where you bashed open the door. Approach the odd strip of light and open the rift, then stop through. Once inside keepers will appear. Kill the keepers and walk to the wall with the glowing yellow symbols on it. The wall will dissolve, and you can now place the 4 gateworms on the 4 pedestals around the room. One to the right, and one to the left will cause new sections of wall to appear that you can run on. Run along to the other side and head to the middle where two more pedestals await. Place these two and a little bit of hell will break loose, but the Shadowman should be visible and your achievement should pop.
There you have it! Mine glitched and popped after doing two rituals, so maybe yours will too. If not, follow the guide and the achievement will be yours.https://www.youtube.com/watch?edit=vd&v=kO2ayjdsx8w