You will get this achievement for defeating Solomon Grundy. This achievement is unmissable!
You can find him in the industrial area, after taking the elevator and going down.
When you fight him, you have to make use of the different environmental things around you (puddles + elctric batarang etc.) Make sure to hit him the last time with an electric shock! This way you will get the corresponding achievement, too.
For more details regarding the other achievement look here:
If you need further information on his location use this written guide by IGN: http://www.ign.com/wikis/batman-arkham-origins-blackgate/Sol...
Or if you need help with the fight itself refer to the video below!
(video credit: House of RM™)
Hope this helps you guys :-)
Any improvements? Please let me know in the comments below!