Gunther
Gunther began as a nameless extra on the show. He was actually hired since he knew how to work a coffee machine. By the middle of the second season, his character got a name, and over the seasons, Gunther became a supporting character.
The One With The Dollhouse
When Pheobe makes a dollhouse out of cardboard, it ends up burning down. Because of this, the props department had to make six dollhouses for multiple takes. And, of course, the houses were all made in a matter of three days.