in chaosrealm you can fight noob somke. Its actually the training with noob somke. Everytime you do it you get like 400 coins. I did it about 10 times and had enough to buy him.

That's awesome, thanks! Do you know where on the map? (letter/nimber)

A semi-fast way to get Onyx koins is in Puzzle Kombat.
I remembered how much it sucked last time having to find koins to unlock characters and costumes, so this time I didn't spend any Onyx koins until I unlocked Noob/Smoke and the Bo' Rai Cho alternate costume.

Here is a SUPER fast way to get them...
1) Go to your options.
2) Set your Arcade level to the HIGHEST difficulty (Leave the puzzle on novice)
3) Go and play puzzle!!!! You get the amount of coins as if you were playing puzzle on the highest difficulty when you are actually playing it on novice!!! (It's a glitch that won't affect your game at all!)

goto options & set "puzzle round ----> 1
you can get like 3000 in 10 mins if your good @ puzzle

Good point. With my hint and if you make the puzzle round wins into 1 match, then you can do it much faster