"5am birthday adventures with my two fav people," Kylie wrote on Instagram.
The supermodel dressed up as Jim Carrey's character from The Mask for her BFF's birthday bash.
Hello, Dolly! Kourtney Kardashian appeared to channel Dolly Parton with her pink fringe jacket and cowgirl boots, paired with a pink hat.
The supermodel daughter of Cindy Crawford donned a witch hat for her pal's party.
For her daughter's party, the Olympic athlete appeared to dress up as Elvira, Mistress of the Dark.
Space Jam! The 22-year-old star was the Lola Bunny from the iconic 1996 film.
Birthday fairy! The Keeping Up With the Kardashians star donned golden wings for her celebration.
The supermodel channeled Catwoman for her Halloween costume.
The beauty mogul went blonde for this Halloween look, donning elf ears for her sister's holiday bash!
The "Golden Hour" singer dressed up as a Dallas Cowboy cheerleader for the celebration, during which she danced alongside Kourtney.