So back in April, I acquired Undertale. It's a excellent game with strange humour and a fun combat system. It's got lots of hidden secrets and multiple endings. Also great music. Would recommend to those here.
http://undertale.com
(You can also now apparently get it on Steam)
So I got it in April. I played through the game twice on my own over the course of a week or so. Then I checked the Internet and discovered two more endings that affect the plot of the game as well as the end. So I did those.
Now the boss of the genocide run is the hardest boss I have played in video games in years. This is a boss that cannot be beat by increasing your character's stats. (And they are almost maximum anyway because you killed everything.) The only way to defeat this boss was skill. I battled him about 50 times. He still lived. I stopped playing the game for awhile as the homestuck ending had just come out and I was consumed by that.
Then in June, I was looking through things on my computer, came across Undertale, and decided to try that boss fight again. Another 50 or so tries, an equal amount of death for me. You may think a boss this hard is frustrating, but it doesn't seem that way. This is a genocide run. You have killed every character up to this point without mercy. You basically deserve the beat down you are receiving.
Now we cut to yesterday. After listening to the Undertale soundtrack on my phone, I decided now would be a great time to fight the boss again. Each attempt is taking longer now, as I can make it most of the way through the fight before dying. After 23 attempts ending with such a close one to actually beating him, no luck.
I decided to take a break. I had lunch. I went to a Pokemon go party in the park across my street. Later that day, I loaded up Undertale one more time. With 1 more try, the boss was finally defeated.
TL;DR: Undertale. You should play it.
http://undertale.com
The final boss of the genocide run provides an excellent challenge.