The best and easiest way:
You need a magic liquid called "Testosterone"
12 months - 3 cycles, you won't be as big as Dwayne Johnson but let's just say you will certainly not be disappointed by your gains.
However, only downside is there's a big chance your junk won't work on and off through this one year, you'll also have bouts of depression and suicidal tendencies. (happens to everyone, can't NOT happen to you.)
Relatively, in the long run, if done right it is safe.
However, these are hormones you're messing with, so I don't know how far the previous sentence holds true.
IMO, This is your only way to get buffed up real quick. Steroids. (And again, don't think steroids are magical pills that you pop and start looking like hulk hogan immediately. You're going to have to work hard even with steroids, (Like work harder than you usually would to maximise the gains while on steroids). That is your only chance in this world to bulk up, and quick!