I've learned that everyone is terrible at sliding puzzles (myself included -- it took me almost an hour to solve this during testing to make sure it WAS solvable), so I think leaving it as completely optional is the right choice.
I unfortunately did not do very good low-level testing on the boss, so if you're not at least level 4 with the 3rd skill, he is unable to be damaged in the jam-version. But, that will be fixed in 1.3 and on (as soon as the contest rating period is over)!
Thank you for playing!