I am starting to like this game a lot but...

I am having a hard time with the coliseum battles. I want to know if there is a way/tip/technique to get more gems in order for me to upgrade my character for obviously, the main reason why I cannot beat the sh!t out of those silly monsters is that my own character is really weak. I am still thinking about buying with real cash as the last resort but if anyone can give me a guide or what not I would greatly appreciate it.

I have uploaded a screen shot of my rank hehe I am in 1st :P

@pamventura: I have a question: after i played the challenge mode, the game and the my phone stops working. I don't know what's happening. I tried to shut down the game. I dont know if the game automatically saves the last level of the game. Always I begin at the start. It always happens to me everytime. What can you suggest? Thank you in advance.