After you've completed the Big Bird replica, how about doing some obscure Muppets such as:
Boppity
Droop
Shaky Sanchez
Lenny the Lizard
Koozebanian Phoob
Green Boppity
Purple Frackle
Dark Green Hunchback Frackle
Flower-Eating Monster
Miss Kitty
Luncheon Counter Monster
Trumpet Fazoob
Fish Fazoob
Whatdyasay Bird
Forcryingoutloud Bird
Ohboy Bird
The Wolf (of Super Sheep)
Quongo the Gorilla
T.R. Rooster
Catgut
A Muppet Cow
A Muppet Sheep
Three Chickens
Three Penguins
Two Lobsters
Brool Minstrel
Murray Minstrel
Wander McMooch
Aretha
Mudwell Mudbunny
Begoony
Poison Cackler
Blustering Bellowpane Monster
Two Inkspots
Tug Monster (of Little Muppet Monsters)
Earl Dragon (of Puppetman)
Harry the Rhino (of Jim Henson's Animal Show)
Two Wickershams (of The Wubbulous World of Dr. Seuss)