This really isn't a brain teaser (ay Kevin? ;) but here we go anyway...

Go east and talk to the tree on your right, go down now (enter the house for some fun) and go down again (or left for more fun) go east, two screens and talk to the old tree. Continue going east and go up. Kill the enemies now as you go along and go east and south twice. Open the chest and go back to the tree you (should've) talked to on the second screen. Use the autograph and a tree will disappear. Go up here and get all the goodies. Now go south 3 times, east 3 times, north, east, north and follow the road, killing all the baddies again. Keep following the road till you come at the Duck from Friends's mansion. Enter it and talk to the duck. Use all the conversation options and go back to the old tree. Talk to him again and he'll tell you about a new duck. Go east and kill it! You've finished the d-mod, enjoy the ending sequence.

Secret room: Go the bottom left screen (the one with a sea-star in the water) and to the bottem left corner. You can walk on the water here. Go east and south and you'll find the secret room. (Be sure to check out the signs!)