Here is the full list of all 9 Final Foe achievements.
You have killed the boss Lord Horror.
You have killed the boss Creature.
You started an online game with a friend.
You have killed the boss Death.
You have scored 15,000 points in Survival mode. Everyone can do it.
You have scored 50,000 points in Survival mode. A little more and you will start to play well.
You have scored 100,000 points in Survival mode. You are an excellent player.
You have scored 175,000 points in Survival mode. You are a monster.
You have scored 250,000 points in Survival mode. How?! How did you do that?! Now you are the king.