The best combinations are:
YYXXXY (Maximum Damage)
YYXXY (Extra Damage)
XYYY (Fast Area Attack + Knock Down)
YXXYXY (Area Attack + Fast Stun + Fast Knock Down)
I found the second chapter with the large group of enemies after ur character and Night Owl split up and get together again is the best to do this (or at least the earliest point with numerous enemies)
The achievement should unlock straight after, assuming you did all the above correctly and quickly.