that method is trading. trading like any other investment method has its own risks but at least you can make an informed decision and calculate those risks. this way there is a bigger chance of success and resulting profit.
I've done many times here in this thread, posting different thoughts about doing trading method.
Yes it has risk but compare to other risky method out there, this is definitely worth to try while at the same time doing your own list of method to earn bitcoin.
Trading For Altcoin is one of the great way to increase bitcoins. There is certain fluctuation within newly launched cryptocurrency. Some of them have good volume against Bitcoin so it can be beneficial for getting bitcoins by trading altcoins.