Question: The Mother appears in which 15th episode of season 2 of How I Met Your Mother?
Context: "Lucky Penny" is the 15th episode in the second season of the television series "How I Met Your Mother" and 37th overall.  It originally aired on February 12, 2007. "Impossible" is the 15th episode of the ABC television series, "Desperate Housewives".  The episode was the 15th episode for the show's first season.  The episode was written by Marc Cherry and Tom Spezialy and was directed by Larry Shaw.  It originally aired on February 20, 2005. Dr. Peter Benton is a fictional character that was a regular on the television series "ER" for its first eight seasons and appeared in two episodes of the show's final season.  He was played by Eriq La Salle.  Benton was often portrayed as arrogant and irritable, but is nevertheless an exceptionally talented surgeon who is passionate about medicine.  It is also revealed that he and fellow emergency room physician Mark Greene had attended medical school together.  Benton's last appearance as a series regular was in the Season 8 episode "I'll Be Home For Christmas".  La Salle's removal from the opening credits as an ongoing regular was in the 11th episode of season 8; however, Benton appeared in the credits of the 15th episode of season 8, in which he is shown talking to Elizabeth Corday, and the 21st episode, in which he appears at Mark Greene's funeral.  He also appears later in season 15. "Oh Honey" is the 15th episode of the sixth season of the CBS sitcom "How I Met Your Mother" and the 127th episode overall.  It aired on February 7, 2011. "How Your Mother Met Me" is the sixteenth episode of the ninth season of the CBS sitcom "How I Met Your Mother" and the 200th episode overall.  This is the only episode of the series in which the episode title was used instead of the usual opening that featured the cast and series's title. "P.S. I Love You" is the 15th episode of the eighth season of the CBS sitcom "How I Met Your Mother", and the 175th episode overall. Angry Birds Stella is a Finnish computer-animated TV series based on the game "Angry Birds Stella" that was produced by Rovio Entertainment.  The first episode, "A Fork in the Friendship", aired on ToonsTV in November 1, 2014.  The series recounts the tale of Stella, along with her friends Luca, Willow, Poppy and Dahlia, as they work their way against Gale, the former friend of Stella, that is the queen of the pigs in Golden Island.  The first season focuses on Gale trying to hunt for the Golden Egg, but, fails as seen in the final episode of season 1, "To The Bitter End".  The second season focuses on Gale returning and trying to hunt for the Golden Egg again, and she succeeded as seen in "The Golden Queen", the 9th episode of season 2.  Also, Dahlia, one of the birds, tries searching for the egg as well for an experiment, but this time, she fails, as seen in "It's Mine!" , the 6th episode of season 2.  Soon enough, the birds realize how dangerous this egg can be, as seen in "Premonition", the 11th episode in season 2, which in when Gale with the Golden Egg, anything that is touched with it, turns to gold.  However, when that happens, another thing turns to stone, the opposite of gold, which causes nature, and even worse, food to be turned to stone as well.  Now, it is up to the Stella gang to save Golden Island before it is too late.  They do succeed, as seen in "You Asked For It", the 13th and final episode of season 2 and the series finale of "Angry Birds Stella", where after a long awful night, Stella and her gang launch the Golden Egg out of the island, never to be seen again.  Gale does not mind because when she saw the Golden Egg after she broke out of the gold in the episode, she ran away, back into her castle. "The Stinsons" is the 15th episode in the fourth season of the television series "How I Met Your Mother" and 79th overall.  It originally aired on March 2, 2009. "Slap Bet" is the ninth episode in season 2 of the popular sitcom "How I Met Your Mother".  The episode, originally titled "Robin Sparkles", first aired on November 20, 2006.  The episode received highly positive reviews and features in several lists of the best "How I Met Your Mother" episodes in the series.  The episode led to two recurring jokes and storylines in the show: "Robin Sparkles", Robin's teenage pop star career, and the Slap Bet, in which Marshall slapped Barney at various points throughout the series. Tracy McConnell, better known as "The Mother", is the title character from the CBS television sitcom "How I Met Your Mother".  The show, narrated by Future Ted, tells the story of how Ted Mosby met The Mother.  Tracy McConnell appears in 8 episodes from "Lucky Penny" to "The Time Travelers" as an unseen character; she was first seen fully in "Something New" and was promoted to a main character in season 9.  The Mother is played by Cristin Milioti.
Answer: Lucky Penny