It's a nice amount of coins.
Here's a 13 hit combo for safe sake. The last hit usually misses but you'll be find because you only need 12.
Spear, Y, A, Up and B, then juggle the person with the Hapikido's longest branch combo. It's tricky to make the juggle hit since that is where the hits rack up but it's possible. Just time it right and Cage will be juggled to death.

I didn't get shit when I managed to pull off a 12 hit combo on Johnny Cage's challenge. I used Liu Kang.