This achievement is going to be on the level "Bridge On The River Ty." Dennis is the frog that needs you to escort him home by lighting barrels on fire that eventually lead to his house, like a trail of bread crumbs. In order to get this achievement, you will have to have completed that escort mission (Home, Sweet, Home.) Once it's completed head over to Dennis's front door and press "Y". If you have done the mission already, but haven't gotten the achievement, you will need to do the escort mission again. The Prompt on his front door will only appear if Dennis is back home. Hope this helps!