This is the last story mission. You fight:
. You will want to use dual takedowns here on the main baddies and you will need to hit left trigger during the fight often to stop some attacks (prompts come on screen). There will be some quicktime events too, my advice there is just to not think they are over until they are over.
also, AFTER you get this achievement, you are put in the center of the main park area. some areas are now closed off but you can mop up the rest of the achievements this way. it is worth noting however if you already took out every enemy pack, you may want to mop up achievements first before you go to rescue your father, as a number of the enemy packs reset after you are thrown back into the 'open world'