For a lot of gamers, video games are a means to relax. They like their adventures nicely played out from start to finish, the plot all laid out and concluded; the villain succinctly dealt with in an orderly fashion.
Whereas for a lot more gamers, they seek the challenge.
The 100% completion rate, the thrill more feats of endurance, strengths to be tested, etc. For some, the main storyline boss isn't enough.
Oh sure, the story may be done, but what else is lurking in the shadows?
The embodiment of the Dark Hadou, maybe? Just how helpful are those merchants that always seem keen to help your quest? How about a grumpy sculptor, or a renowned actor?
The thing with secret bosses is... well, they're always hard to find. And like most secrets, they can sometimes come out of nowhere and ruin your day. So sharpen your blades and fill your flasks, as many of these require specific methods to bring them out of hiding.
Seeking them out also means you're signing up for a level of skill the base game doesn't go near, and that can be pretty damn awesome.
10. Akuma - Super Street Fighter II
We'll kick this list off with one of the earliest and best examples of secret bosses, way back before the days of Capcom's nefarious practice of purchasing extra characters took over.
Akuma, or Gouki in Japan, is the brother of Ryu and Ken's master, Gouken. Seduced by the powers of the Dark Hadou that eventually corrupted, he discarded humanity and become the malevolent force we all know as Akuma. An anti-hero to Ryu in a way: whilst Ryu wants to test his might around the world, Akuma seeks to crush anyone that may challenge him.
This is the meta-test to unlocking him in battle: Akuma won't appear for anyone struggling their way through the world warriors. Like a fussy date, he won't show for anything less than perfect. Quite literally, as you need a few of those (and some super endings) to have him replace M. Bison in the final fight. Y'know, instead of the already double 'ard M. Bison.
It was a true test of strength and skill back in the early days of Street Fighter. Now you can just get him with a season pass.