"That was too Easy." phrase
“That was too Easy.”  can simply be translated as "那也太容易了" 

However, in a mocking manner, you can say: 

不外如是 (It is unimpressive)-- It is a very insulting phrase, saying that is to look down upon someone

這就完了? (just like this, you are finished?) --implying the other guy cannot provide tougher challenge to you