Mr. Shifty

This isn't cumulative I'm afraid, so you have to pin 5 enemies to a wall with a single trident. The best place I found to do this is when you first get the trident in Stage 4 "Defiant" (getting the trident is unmissable since you need to throw it through a laser grid at the generator).

From here, clear out the few enemies, then go into the next room. You're in the right place if there are 2 large statues right next to the door you come in. You'll notice a wooden door between you and a whole bunch of enemies. Leave this door unopened (shift through the door or wall to get to the other side). Now, round up as many enemies as you feel it is safe to do without getting hit (keep an eye on how many shifts you have left), then shift back to where you came in, again leaving the door untouched.

Then, stand behind the door. If you've left the door untouched the enemies won't shoot through it, meaning they will all try and run through the door to get to you. With the door still shut, wait until the last possible moment, then throw the trident at the door. With a bit of luck, there'll be 5 enemies on the other side of it which means the achievement will unlock! If not, simply let a surviving enemy kill you and you'll respawn right by the 2 large statues ready to try again.

Hope this helps and good luck!