The first four clue phrases in each set below conceal a word that is hinted at by the last clue. What is the answer to the last clue and how does it explain the hidden word?

1)
A. MYTHICAL MONSTER
B. FISCAL MATTER
C. CRITICAL MASS
D. CLERICAL MISTAKE
E. SERENITY

2) 
A. BARGAIN FOR
B. TIN FOIL
C. JOIN FORCES
D. RAIN FOREST
E. TIP

3)
A. ROMANCE
B. DEMANDS
C. ADAMANTLY
D. HOLY ROMAN EMPIRE
E. BUSINESS DEAL ARRANGER, PERHAPS

Answers:

1. SERENITY is inward CALM
2. TIP is inside INFO
3. MIDDLEMAN is MAN is in the middle