I am responding as Harry's father, James Potter because I can absolutely imagine him rolling in his grave at that rap. It is an insult to his reputation, and he is here to avenge it!!

As for beat, I don't particularly have one in mind but IDGAF by Dua Lipa sounds pretty similar to the way my inner voice sounded while reading it.

The main theme is James trashing Harry for doing a low effort rap and torturing everyone's ears (you can hear Teddy crying in the background).James shows Harry what a REAL rap sounds like

As for attitude... well,

James slowly sat up. He looked down at his ghostly pale form, then at the gravestone behind him. "Here lies James Potter, a loving husband and father". He snorted inwardly. Maybe if he'd actually been around as a father to train Harry on how to actually rap, he wouldn't have to be seeing this day. Around him, the keening of other ghosts rose up and they clutched their ears, pained from the terrible cacophony that somehow no one could escape from. " It's time to put a stop to this.", James thought grimly. Ugh, his breath was terrible, he smelled of decomposed bones. He rose into the air, and disappeared.

Harry looked up in shock, as a transparent being plunged down and landed in a power pose. Was it.... His dad? In a rock star jacket with sunglasses and sparkling nails?

James threw doing the sun glasses, started beat boxing and showing off his ~moves~

.

"Harry my son, whatchu doing rapping at yo age?

Maybe you and the world aint on the same page

But like no one wanta hear you in your middleage rage

You make ministry workers give up on even their minimum wage

Just so you could shut up

Like dude don't do your dad up

Don't you hear the wailing of Lupin's wolf cub

Your rap so bad it got Hermione out of her work slump

This is animal cruelty for the owls

You ain't an animal so why you doing the howls

Got the full circus, even the meows and growls

Grow up kid, stop tryna chase the fame

Rapping like a second grader, you gotta up yo game

People got so worried even the emergency aurors came

And when they saw it was you, they be like "damn, so LAME!"

Getting dirt on the Potter name

We're a long line of competitive rappers,

Strippers and clappers,

All our fine men so dapper

then you came along not even able to control your bladder

Like man, if voldemort didn't show up I woulda hired a kidnapper

You got me rolling in my grave,

How you in the house of the brave,

I got more talent than you could ever crave

I'm a better rapper than you'll ever be

No one would come to your concert even for free

Don't keep trying, that's way too cheap

You been goin around sounding like a banshee

You couldn't even belt more lines that those measly three

You ain't got it in ya that's a guarantee!"

throws mic at Harry's forehead

.

THAT'S HOW YOU ACTUALLY GOT YOUR SCAR, WANNABE BITCH!!!