The most epic boss fight that I had is actually a tie between 3 bosses, all from the same series.They are Henry Cooldown, Maragret Moonlight, and Alice Twilight from the No More Heroes series.
Henry was just awsome. The fact that he is your twin brother who has an Irish accent, he marries Sylvia Christel (The woman that you try to make out in the game), has fast attacks, a ton of HP, and an awsome one hit kill where he stabs you, throws you in the air, slashes you upwards which sends you higher, then throws you back to the ground where you get impaled by his beam katana, and Henry lands on top of the beam katana causing the ground to break. All of this by a non-super human person.
As for Maragret Moonlight not only was the pay-off to fight her excellent, which was an long level that took a long time to beat, but it was satifiying. She dresses up like the grim reaper (Just without a skull head and black robes), has sycthes that can turn into a gun. She is quick and deadly, she'll also teleport to a place where she can shoot you. Not to mention that the background song is amazing, not only does it explain why she is an assassin, which the reason is because she wants to kill people who she believed are sinners, but the song also mocks Travis Touchdown by calling him something far from a hero.
Henry Cooldown and Maragret Moonlight are perfect examples of a memorable boss fight. However a great fight and being memorable doesn't make them the best. The best one out of all three and shines brighter than both is Alice Twilight.
Alice Twilight is a prime example of having an excellent fight, excellent memorablitiy, perfect set up, and having an excellent of everything. As much as I talked about how much Henry an Maragret are great, how can Alice beat a guy who is fast, cool, an can crush the ground without super human powes, and a girl who dresses as the grim reaper and kills people who she believes has sinned? First is her personality, she is honorable, and just like Travis she questions why she is an assassin and killing people. If that is enough to be epic for you, then how about this. She weilds not one, not two, not three, not four, but she wields five beam katanas and a robotic tail. It's sun down, two people equal in skill fight with swords in what could be for nothing. This fight could be explained as one of the, if not THE, greatest sword fight in video games (In my opinion). She has a ton of HP, great personality, awsome attacks, and overall an incredible boss.
I just wished that you didn't kill Alice and that she was the final boss of the game rather than that pretentious, ungrateful, spoiled, bratty, self-rightous, manipulative, annoying, cheap, lazy, unfair, and unlikeable Jasper Batt Jr.