For this you will need dlc pack:
Lego Movie Aquaman Level Pack 2From loading into the hub press the
Back button and then press
To:
Level SelectScroll Down to the Level “The Final Battle” *** Spoiler - click to reveal ***Complete this very short level by freeing some sea creatures, defeating some Trench creatures, solving a short power supply puzzle and then moving onto the Sea Vessel.
Once you are aboard Orm will send in a few Murk enemies to defeat along with mashing 
to remove his 6 hearts of live then levels....
Pop achievement unlocked.
Congratulations!
Happy Hunting