Meltlillith (メルトリリス) is a character resembling Sakura Matou and BB (Fate/extra) in Fate/Extra CCC. She has giant, pointed needles for feet, a penchant for fighting, and an uncanny amount of fighting ability. Her face resembling that of BB is also a trait shared by Passion Lip.
Source: Type-Moon wiki
She is introduced as a limited servant in "Fate/EXTRA CCC Collaboration Event" event in April-May 2017. Her class is "Alter Ego", a new servant class introduced in the same event based on her role in Fate/Extra CCC.