So I really like heroines that are complex and hard to understand. Could anyone recommend me a drama that involves a cold female lead with a dark past or simply a drama with an odd unusual heroine? some examples that I've seen include:

Cinderella's sister

Alice in wonder city

miss ripley

my love patzzi

summer's desire

hard nut!

otenki onee-san

keizoku 2 Spec

the snow queen

Flowers for My Life has a very unusual heroine.  Not cold, exactly, but definitely odd and not at all a typical k-drama heroine.  And it's a fantastic drama, to boot.

Someday (2006 K-drama)? I hesitate to recommend it as a drama, but the lead girl is pretty weird (the synopsis even calls her cold and aloof!  So there you go).  But she's a likable weird, at least for most of the drama.
The first drama I thought of was Birth Secret. It's an amnesia drama and may not be your cup of tea, but I felt that the heroine had a lot of similarities to the ones you mentioned that I've seen (played by Sung Yuri, same as The Snow Queen). 
If you like crime procedural the heroine in H.I.T (Homicide Investigation Team) is someone I would describe as cold and determined (that drama is highly underrated in my opinion). 
And if you want a really mysterious female lead you can always go with The Suspicious Housekeeper (I've only seen the Korean version but I thought it was very well done). 
Secret Agent Miss Oh was the first to come to mind since the female lead was very unusual and different from most dramas I've seen.
I Love Lee Tae Ri's lead was straight up cold though.
thank you for all the recommendations! They all look super interesting. you guys are awesome! stay classy =)
There is also Cinderella's Sister. 
Padam Padam: I've only just started it, but the synopsis describes the female character as cold, so far I can say that's accurate (I'm about 4 episodes in), although I don't think she's the stereotypical cold character. I have to say the male main lead is quirky, unlike any male lead I've ever seen before. 
What about The Queen's Classroom? The homeroom teacher in question deploys extreme method to manage her class, but there's logic behind it (which the students came to understand too, eventually), and she also has a dark past (told in the special episodes) that made her become the teacher that she is.
  coldish leads
Akumu chan
Tantei no tantei
Piece
Orange days
strawberry night
Hi my sweetheart

  odd unusual
Date
Hi, I was looking for the same kind of female lead.

History of the salaryman
: The female protagonist is unbearable, bossy, rude and conceited, and she is the granddaughter of the CEO of a company. Only the two male leads can see the reason for her behavior and all the pain she hides.

This is an awesome kdrama, and has one of the best performances of Jung Ryeo Won.
That Winter, The Wind Blows and Innocent Man to an extent.
thanks! Padam Padam and History of the Salaryman are exactly what i've been looking for. I definitely plan on watching alot of the other ones mentioned as well since they all look pretty damn awesome. Thanks so much for the recommendations! 
Flower Boy Next Door
Yamato Nadeshiko Shichi Henge
History of the Salaryman

The Innocent Man ( Joong Ki n Moon Chae Won) 

Cinderella's  sister ( Moon Geun Young )

That Winter The Wind Blows ( Hye Kyo n In Sung)

Bravo My Life ( Jung Yoo Mi N Hyun Woo)

Just Between Lovers ( Junho 2PM n Won Jin A )

The main girl from Yamato Nadeshiko Shichi Henge is the meaning of odd lol I loveee this drama, definetly recommend it to you..

Age of Youth first season, this drama has a lot of ladies and the senior of them was so real and hard to understand for others.. 

Flower Boy Nextdoor has a shut-in female lead also

A Coin Locker Girl, movie but we have 2 complex woman who are excellent at acting^^