Demitri's Midnight Bliss special attack hides many Easter eggs if performed on Street Fighter characters in Capcom Fighting Evolution
Within the Darkstalkers series, there is a character known as Demitri -- a vampire. His special attack, the Midnight Bliss, is a particularly interesting one.
Through this attack, Demitri transforms his opponent into versions of themselves that is either a gender swap or comedic. He'll only transform males into females. He doesn't appear to transform females into males.
As pointed out by Miðgarðsorm on the Shoryuken forums, there are a number of easter eggs found inside of the Capcom Fighting Evolution game. These tend to pop up when Demitri performs this peculiar attack upon Street Fighter characters.
Something that is indicated by this user is that some characters have two different transformations if you use a different input to perform this special. A number of characters appear to only have one transformation, however.
So starting with Ryu, he transforms into a young girl. She is holding a silver object.
This girl actually appeared in the Street Fighter Animated Movie.
For Guile, he is basically just transformed into a female with an American flag bikini.
Being that Zangief is Russian, he turns into the "tangerine vending Russian girl." This character is loosely based on a Russian cartoon character known as Čeburaška.
M. Bison changes into a female version of himself.
Sakura gets a gym teacher outfit. You might recognize this outfit as the outfit Sakura was sporting for her ending in Street Fighter 4 (obviously SF4 referenced this material rather than the other way around).
Guy is also just a female version of himself. Interestingly enough, his head is basically just placed on Maki's body (another character that appeared in the Final Fight series).
Demitri is also able to change Guy into Shadow Girl from Gotcha Force using that special input.
Rose gets transformed into the Jojo characters known as LISA LISA! and Enya the Hag.
Karin appears in an outfit that was apparently based on Reika Ryūzaki, from the manga "Ace o nerae!"
Alex has a female variation of himself and also transforms into the character Patricia, who appears in Street Fighter III: New Generation.
Yun is transformed into his girlfriend, Houmei.
Urien is changed into a girl in clad and shimekomi fundoshi.
Chun-Li is transformed into her Alpha 3 costume and her pocket fighter sprite.
As for Ingrid, she appears in her Sweet Lolita attire.
These are only brief explanations on my part which are based on the more elaborate explanations by Miðgarðsorm. Head over to the Shoryuken forums to get more information on these transformations.