I've spent the last three days mired in Level 5. I played through the level over and over almost always making it to the Grim Reaper and always getting utterly destroyed because of his obscenely difficult, and frankly, rude fighting style. He floats around the screen while miniature sickles fly around randomly with no pattern. They are extremely difficult to hit with the whip and the Grim Reaper seems to have no pattern either, so it cannot be memorized.
After the actual boss, the second hardest part is the hallway leading up to him. There are these knights that take about 10 hits to kill and back away from you as you approach. So you have to jump toward them to gain any ground. While you're worrying whether or not they'll launch an axe at you during your jump, there are also Medusa heads flying all around the screen. Oh. And everything that hits you takes away 1/4 of your health bar. So 4 hits and you're dead. So even if I made it to ol Grimmy, I would really only have 1 or 2 hits left in me.
I finally got frustrated and watched a Youtube video of someone playing through the level and discovered that the Holy Water is a must. It stops the Knights in their tracks. It stops the Grim Reaper in his tracks and even prevents him from summoning the mini sickles if you do it fast enough. But it looked a little cheap - I wanted to do this on my own - just me, my whip and my skills.
That got old mighty quick and I decided to try the Holy Water approach.
I soon realized the inherent challenge in that. The Holy Water is the very first sub-weapon you get in this level and it doesn't appear again after that. So you have to:
1) Not die if you've passed the first check point
2) Avoid touching any other weapons lest you lose your Holy Water
3) Find both Level Up modifiers to make them effective
I was finally able to make it through the entire level without taking a single hit and reached the Grim Reaper with about 75 units of fully maxed out Holy Water. And I shoved every single one of them down his stupid, dead throat.
So even though I didn't kill the Reaper with the whip, I still felt accomplished for getting through the entire level on one life.
Then I started Level 6. Then I wanted to find the level designer and punch him in the forehead. With a gun.