Okay, found a way past. It doesn't actually involve killing a baby on a spike trap.
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×Take the decoy potion on the right first and get two babies horizontally in line with it, cutting the tar on the left.
Now my problem is getting enough babies.
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×As far as I can tell:
-I need a decoy for the gel blobs
-I need to do a double-cut on the northeast blob
While I can set up a decoy for a double-cut on the northeast blob easily enough, I can't see a way to make the cut on the turn before that without getting killed.
Also I'm not sure how you get the gel babies into position after placing the decoy there, but I haven't actually attempted that part yet so I'll worry about it when I get there.