I have a feeling that RMT3 will take some time, so here's 4.
I am the bane of evil, the savior of light.
Do not provoke me, as you’ll lose the fight.
Inside the strongest I am found,
even when tossed to the ground.
I can be selfish, or even rude,
but do not blame me, though I am crude.
I can change someone for the better or worse,
even to the point of needing a hearse.
I’ve told you about myself,
something that cannot be put on a shelf.
Now riddle me this samurai.
Tell me, what am I?
THE SAMURAI HAS NOTHING TO DO WITH IT. IT'S SIMPLY THERE TO RHYME.