This is a scene from Transformers: Beast Wars episode 17 "The Trigger" Part 2, she is called Blackarachnia.
If there are more transformation scenes like this, Please let me know and share it here !!
(female only) :3

https://www.youtube.com/watch?v=Qizx9n-rtiI

[/youtube]https://www.youtube.com/watch?v=Qizx9n-rtiI