In Season 7, Episode 3 ("Teen-a Witch") Tina dresses up as a witch between two slices of bread to form a "sand-witch" for the school's costume contest.
When Linda takes the kids to go trick-or-treating in the episode "The Wolf of Wharf Street" (Season 8, Episode 3), she decides to combine famous singer and actress Cher with a police sheriff. Fun fact: This costume also came with handcuffs, but Linda forgot them at the apartment before she left. This, however, comes in handy for Bob later in the episode - as he uses them to restrain Teddy to the coffee table.
Season 9's Halloween episode (Season 9, Episode 4 - "Nightmare on Ocean Avenue Street") is full of great costumes from the Belcher kids. This one's pretty simple, Tina just takes a nun costume and a briefcase - and boom!
Also from Season 9, Episode 4 ("Nightmare on Ocean Avenue Street"), Gene combines two famous Andrés to create his Halloween costume: André 3000 of the musical duo Outkast and the late wrestling legend André the Giant.
Lastly from "Nightmare on Ocean Avenue Street" (Season 9, Episode 4), we have Louise as "the dragon with a girl tattoo" - a twist on the novel "The Girl with the Dragon Tattoo" and the film adaptation of the same name. Though, given the dark nature of the source material, one has to question how a nine-year-old girl knows of it. Although, given that this is Louise we're talking about, perhaps we shouldn't be surprised.
Next, from the episode "Pig Trouble in Little Tina" (Season 10, Episode 4) we have Gene as "Fiona Apple Sauce". While outwardly a just a combination between famous singer-songwriter Fiona Apple and apple sauce, Gene explains that he's actually going as Fiona Apple's "saucy aunt'. That means this costume is extra special - it's got lore behind it!
The episode "The Pumpkinening" (Season 12, Episode 3) is also full of great costumes from the Belcher kids. For Tina, she combines the famous fictional detective Sherlock Holmes with the equally famous urban legend of the Loch Ness Monster. It's half sea monster, half sleuth!
Also from Season 12, Episode 3 ("The Pumpkinening"), Gene's costume is a mashup of a gladiator and a graduate. As Gene states, his costume is, more specifically, "a gladiator who just got his master's".
The last costume from "The Pumpkinening" (Season 12, Episode 3), Louise dresses up as Peter Pan but with a bit of a dark twist. Once more referencing media that she is definitely should not be seeing at her age, Louise draws an eye on each of her palms, like the Pale Man from the 2006 Guillermo del Toro film "Pan's Labyrinth". Understandably, she freaks her dad out when she does the iconic pose from the movie.
Our very last costume doesn't come from the Belcher family, but rather from Louise's friend Jessica in the episode "Apple Gore-chard! (But Not Gory)" (Season 13, Episode 6). Jessica's dad is apparently a fan of British rock singer Billy Idol and American singer-songwriter Billie Eilish. So, Jessica decided to combine the two musicians into one costume for the school's costume parade. This costume idea's not bad for a girl who, prior to their friendship, Louise once described as "bland" and "boring".