×There are two potential approaches I can see. I'm not having any luck with either.

Option one: Skip the west mud, head to the trapdoor, turn sword, destroy the east mud, find some way to use mud babies to move the mimic further west in his section.
Option two: Destroy the west mud, use babies to separate the mimic from Beethro, turn the mud to gel with Beethro, get enough distance with the mimic that you can stand on the black wall while he's on the trapdoor, destroy the mud on the black wall, get the mimic to your west, destroy the last blob of mud.

Option two seems more in line with what this level's involved so far. But I haven't been able to get enough distance. In theory I think I should be able to, but I can't walk diagonally past the gel blob and that restricts where the mimic can be at that point.

So what should I be doing here?

×As you've probably noticed your biggest issue is sword positioning preventing you from stabbing the mud and getting past the black door. I just tried this out (since it wasn't my original solution) and there is a way to pull it off, but I'll look at option 2 instead of explaining how I did it.

×As you've also noticed, there is no one spot you can leave the gel babies and manipulate the mimic correctly. Since you'll probably have to kill one of the babies you've really only got one. If only there were a way to make him stay in two spots at different times.