Melodic Song into Song with lots of drive

The title may not explain what I'm trying to say very well but this is basically what I'm getting at... I have a mellow melodic song such as the build-up for strobe by Deadmau5 and I'm mixing into a much more energetic song such as Alcoholic by DADA Life (I don't know if those are mixed in key or not but just for the sake of the example) sometimes this works sometimes this doesn't because you have the mellow synths of strobe going into an extremely hard electro bass noise in the next song it doesn't really work that often if you just simply mix them without any kind of on the fly effects or looping. What technique do you guys find best for doing this?

Dont do it,
Work it up.

i would build it up and save that track for later... though adding FX like a filter, a reverb and using a loop roll or working up beatmasher into the drop from the second song could work if you absolutely have to!

that is wayyyy too subjective of a question to be answered over the internet.
what may work for one combo of songs wont for another, this really is something only you can answer for yourself thru trial and fucking error man.

At last, I don't understand what you say...

hi mmoxe, meet jesterhammer.