All gameplay was taken straight from Twitch Livestreams, so keep that in mind if you hear on-topic commentary, off-topic commentary, and complaining about personal incompetence. That said, also keep in mind that this is far from a flawless run for the level, but it gets the job done.
P-Ranking a boss requires you to beat the boss without getting hit a single time.
The 4th boss is definitely the most action-packed boss out of the 4 standard bosses in the game in my opinion. He's pretty quick and the 2nd phase in particular amps up the heat quite a bit. Like the other bosses though, he primarily requires pattern memorization. The only additional recommendation I would give is that he can be generally attacked before he starts up a new move. For example, if you look closely at 0:32, I hit him before he goes into the frog state and then quickly followed up after he landed for a solid 1-2 punch. This gets me out of this particular attack a bit faster than normal. If a boss is living for a longer period of time, then they'll have more chances to hit you as you would expect. Hit him hard and fast.
Chapter -
0:00 - Level Start
0:17 - 1st Phase
1:54 - 2nd Phase
3:07 - 3rd Phase
3:41 - Strike a Pose
And as usual, feel free to drop by the stream if you'd rather see streams compared to YouTube shenanigans.
-- Watch live at / tminator64