2. The Write Stuff!

The Greenies start working on the script for their mashup musical with help from Chris Colfer, who teaches them that words are important.

3. Singin' in the Room

Josh Groban visits the theater for Julie's birthday and shows the Greenies how to sing from the heart -- and in perfect harmony.

4. Hello from the Ogre Side

When a disappointed Peri learns she'll be playing an ogre, Alec Baldwin reminds the Greenies that acting is all about pretending.

5. Barre None

The Greenies hit the barre for a master class with married dancers Tiler Peck and Robert Fairchild, who've come to show them some ballet basics.

6. Write … Write a Song

Sara Bareilles stops by to teach the Greenies how to make their own melodies. But combining music and lyrics takes serious teamwork.

7. Morning at the Improv

The Greenies attempt a run-through, but their focus is on the fritz. Can improv expert Ellie Kemper shape their chaos into something amazing?

8. Quacktice Makes Perfect

When Fizz asks master violinist Joshua Bell for musical guidance, the friends learn that playing an instrument takes tons of practice.

9. Send in the WOW

Julie sends in a clown -- professional showman Bill Irwin -- to help calm Riley's fears about being funny and teach the gang about circus arts.

10. Rhythm Is Gonna Get You

When the percussion instruments they ordered go missing, the Greenies are forced to improvise with a little help from the cast of “Stomp.”

11. Costumer Service

Special guest Tituss Burgess shows up with an array of colorful costumes that help the Greenies bring their characters to life.

12. The Mess Rehearsal

The Greenies' first dress rehearsal is a mess rehearsal. Can guest director David Hyde Pierce help them sort things out before curtain call?

13. Mash-Up: The Musical

It's opening night, and the Greenies are ready to share what they've learned with a live audience -- including VIP patron Mrs. Edna Brightful!