Acting for Two: Almost any episode featuring Crais, as the actor, Lani Tupu, also voiced Pilot. Also Wayne Pygram, who plays both Scorpius and his mental clone, "Harvey". While Harvey starts out being little more than a copy of Scorpius's personality, he later develops a personality of his own in seasons three and four, taking on knowledge and appreciation of popular Earth culture from Crichton's mind and becoming a less antagonistic character concerned more with his and Crichton's survival. Numerous episodes feature both Scorpius and Harvey. And in the "Look at the Princess" storyline, Jonathan Hardy, the voice actor for Rygel, appears onscreen as one of Moya's alien "Builders" (his eyebrows are the giveaway).
In addition, some of the guest starring actors and actresses who have played alien characters in one season end up playing other alien characters in a later season. One of the biggest examples is Francesca Buller, wife of Ben Browder, who has played in all four seasons of the show as alien characters (M'Lee from "Bone to Be Wild" in Season 1, ro-NA in two of the "Look at the Princess" three-parter in Season 2, Raxil in "Scratch 'n' Sniff" in Season 3 and Minister Ahkna in four episodes of Season 4. Minister Ahkna is the only character she has played for more than one season, having to have been included in "The Peacekeeper Wars" mini-series).
In Season 3, Ben Browder started pulling double duty as John Crichton during the episode "Eat Me" until one of the Crichtons dies in "Infinite Possibilities (2): Icarus Abides"
In the Season 2 episode "My Three Crichtons", Ben does triple duty as Crichton, Caveman Crichton and Future Crichton
In the Season 4 episode "Prayer" Jason Clarke is billed as the Scarran officer, Captain Jenek. He also played the role of Lechner (Aeryn's fake lover) in the flashback sequences in the same episode.
Actor Allusion: When the crew lands on Sykara, Crichton quips about how much it reminds him of Mad Max: Beyond Thunderdome. When Rygel goes, "Huh?", Crichton adds, "Don't worry, no one saw the third one." Jonathan Hardy, the voice of Rygel, was in the first Mad Max movie, and the actress who plays Zhaan, Virginia Hey, was featured in the second movie The Road Warrior.
Executive Meddling: A rare good example, as the newly-appointed head of the Sci-Fi Channel was a big proponent of Farscape's 'edginess'. This was partly due to the presence of Jim Henson's moniker, not to mention the family-friendly puppets; both of which were unnerving to a company that was re-styling itself as an adult network.
On a much less positive note, the heavily-derided opening of season 4 was the direct result of SciFi insisting on slowly reintroducing the cast for new viewers. Additionally, the series was under contract for a fifth and sixth season, but SciFi initially tried to back out of the contract by shortening the order to a 13-episode half season. When the showrunners attempted to fight for the original contract, the series was summarily canceled. And all of this after the fourth season finale cliffhanger had been filmed, leaving no time to write and film a new ending for the series.
Throw It In: Much of the more comedic lines were reportedly ad-libbed by the actors. Also other little things, such as Crichton's nickname for Chiana ("Pip") being Ben Browder's nickname for Gigi Edgley.
Chiana was originally not part of the cast, and her first appearance, she was supposed to die. However, the cast and crew liked her so much they let her live and made her a main character. A side effect of this was that Edgley decided to keep the exaggerated head movements she needed to do in her first appearance thanks to her restrictive contact lenses, despite them being replaced with more comfortable ones.
Melissa Jaffer joined the regular cast as Noranti at the end of the third season after playing two different guest roles in the second: the aged Nilaam in "Vitas Mortis" and the female Pilot in "The Way We Weren't"
Linda Cropper played the female Plokavoi... Plokavian interrogator in "The Ugly Truth" before being cast in the recurring role of Xhalax in the third season.