Solution to M:
Every correct solution gotten in Act 2 gave 2 pieces to fit onto the shape given by the meta puzzle.
Successfully piecing the shape together yields this solution:
Each shaded horizontal row is a word with a letter missing. However, there are two different letters that could make a valid word for each row.
-SLE_T can be SLEET or SLEPT
-RE_IVED can be REVIVED or RELIVED
-AB_DE can be ABIDE or ABODE
-QUIL_ can be QUILL or QUILT
The missing letters of the first words spell out evil, and the missing letters of the second words spell out plot. Of course, the possibility of answering plotevil is there, but the answer the other way around makes a little more sense.
EVILPLOT