The Phantom of the High School Musical was the disguise of Coach Hayes. He wanted to disrupt the Talent Show which was going to take up the time of his star player from the Athletic Competition. He appeared in Scooby Doo! First Frights. The monster is a play on The Phantom of the Opera, he even has the same white mask.
Unlike the other bosses in Scooby-Doo! First Frights, the Phantom sings during the first phase of his fight,
Why hello, here you are, and how lucky you're the stars! but it just might not end so well for you. Could you be that mystery crew? you know I'll see my plans through, what I'm saying is, No talent show for you! I don't know why they even put it on that day! Oh No!, what I say? come, now skulls, that's your cue!, show these kids what you can do! Why don't you kids just go home? What are you doing here alone!? I'm going to- call your parents on the phone, That's right! don't you think they'll get a fright, when they hear your out at night, and not tucked into bed tight! yes, I'm going to rat on you! Cause that's just what phantoms do! oh, and you are just in time! To see the school's defensive line! Stay away from that device! what if you turn out the lights? (hint on how to beat the first phase) JUST GO! Why do you brats have to be so bold? have you kids even solved, the grand mystery I behold?, I don't think!, Ha!, more like "Mystery Stinks"! that talent show will be no more! You kids have really droped the ball! come, now skulls, come out and play! It's time to wreck their day!