One way of getting all the alternates costumes is playing the arcade latter or buying them in the Krypt. Once you beat the ladder, you will unlock an item/key that unlocks the characters alternate costume in the Nekropolis. If you play tag ladder you will ONLY unlock the 1st chosen character alternate costume but you will unlock both endings.
*Note: Cyber Sub-Zero does NOT have an alternate costume.
You do NOT need Mileena's 3rd Costume (Flesh Pit)
Here's a list of where you can buy the costumes in the Krypt.
http://www.xbox360achievements.org/forum/showthread.php?t=30...