Here is the full list of all 12 Watchmen: The End Is Nigh achievements worth 200 gamerscore.
Complete the game in less than 80 minutes in one session, without restarting from a checkpoint.
Go unharmed for an entire level, without restarting from a checkpoint.
Complete the game in co-op mode.
Complete the game in Nite Owl mode.
Find all abilities and pickups in Nite Owl mode.
Knock 100 people over, by throwing other people into them.
Eliminate 20 bad guys in 101 seconds.
Complete the game in Rorschach mode.
Find all abilities and pickups in Rorschach mode.
Perform 250 finishing moves.
Perform 200 counter attacks.
Dodge or block 25 incoming attacks.