WARNING THIS ACHIEVEMENT IS BUGGY & MAY NOT POP FOR CERTAIN GAMERS, I HAVE PUT THE WAY I RESOLVED MY CHEEVO TO POP RequirementsLego Movie DLC Level Pack 2Load up the level which called
”The Final Battle”This can be worked on during your first play through if not load up freeplay after completing the level for your first time.
As soon as you spawn in watch/Listen to the cinematic with Aquaman & Orm then free the Seaman On The left then Orm will send in his minions which are the Trenchman.
Now select
Mera and attack and kill 10 of the below enemies I advise to be quick mash your

attack or press

then

again to pick up and slam as your coop AI will defeat them too.
There are more than 10 which attack but if your coop buddy beats you to then you may need to load this back up again.
Image below changed both characters to Mera just encase and could quickly swop locations for attacks Mera below attacking the Trench enemies:
*At the moment there seems to be a few issues with the achievements popping, I advise completing the requirements and quit & saving then doing a console hard re-set which helped pop mine.
If this fails to work, there is another method to try, so start a new game on a new save complete the first level. When you exit the Jokers Fun House in his Truck you then should be able to press the back button to select the level select and load up the dlc level again as soon as the level loads ups and kicks in the achievement should just pop as long as you have met the achievement requirements.. Thanks to checo316
Then pop achievement unlocked.
Congratulations!
Happy Hunting
*Please leave FB on the actual guide not just if it didn’t pop for you this is a game issue not a guide issue Best of Luck!*