If you are reading this, chances are you faced the same issue i did when i first started the game. Playing single player (as i only own 1 keyboard) I noticed my attack precision was less than half of the Bots. I was stuck with basic right,left,up,down, diagnals. Which isn't bad, but it defanitly hurts your ability to react to some situations.
I played on just my keyboard, as i thought it was the ONLY way to play without a gamepad. But to my suprise I learned i could use my mouse as single player. This is incredibly simple yet it is easy to miss.

When you start the game up your mouse is unusable at the main screen so use your mouse to start the game up. When you are presented with the 4 "Insert Coin" texts, simply click your mouse instead of pressing enter on your keyboard and presto, your game is now totally mouse controlled which provides far easier maneuvering in my opinion.
To my suprise after switching to my mouse i found beating the end boss far easier. So good luck, and be wary of the IRS.

Once in game your character will follow your mouse whether you are human or ghost.
Left click to attack (swing sword, shoot bow). And Right click for your special (default roll).
While ghosting just move over a summon ring and click the attack button to activate it, the monster controls are the same as human.
A note to make is that though this is more percise, there is more room for error. With a keyboard you will stop immediatly as you stop pressing a button,but with the mouse your movement speed will detemine how fast you get to the point your mouse is at, and it will keep moving your character till you reach that point.