Calling Dark Souls unreasonably hard is almost an understatement, tmost of us would likely agree. But there are those who feel an added challenge is need such as Twitch user Bearsly who actually completed the whole game using only a Rock Band guitar.
To be able to do this, he created his own control scheme (PC version played) and every little part of the guitar from whammy bar to the Star Power had to be used. Since there isn't enough buttons on the guitar, he had to limit himself by only being able to walk forward, backward and right, and the camera could only be rotated to the left. Heavy attacks couldn't be used or blocked.
Playing through the game took Bearsly around eleven hours. When he finally med the final boss Gwyn, Lord of Cinder, it was completed in only three attempts, turning out to be one of the easier parts of the playthrough.
Next in line for Bearsly is beating Dark Souls 2 with the same set up. Best of luck, Bearsly!