About the MKX, it's because I didn't know how many versions you'd make :P, it's my way of saying "Mark anything", or saying something has one version.
About the challenge, it would take ages because of how bulky she is, but it would be fun to fight something that can't die in a hit.
About indestrucible, what if you found two versions: One that had no shield, but could be killed by chipping at her armor or destroying her core, and one that has a shield, can block any attack, but gets knocked back by hits, what I'm thinking about is having her (And some respawning cannon fodder) in a map with a lava pool on the end, you have to push her while avoind endless waves of weak enemies, when she hits the lava, she dies and all of the other enemies would as well.
Also, fire, maybe she could be rather fire resistant so you don't have a simple tactic against her, but fire would still be effective.
Maybe her weak point should be the core, making precise strikes key to beating her without, well, taking ages to chip at her body, maybe it could be her only weak spot.