Master Frown was trying to one-up Unikitty and her friends because of their long lasting rivalry. But, Master Frown was mostly just jealous. And when he found out that Unikitty and her friends were also starting a band. He was outraged

”SO THEY JUST- STOLE OUR IDEA?! BROCK THEYRE ALREADY BECOMING A HIT, HOW THE HECK ARE WE GONNA GO AGAINST THAT?!”

Master Frown exclaimed loudly. He wasn’t allowing Unikitty or anyone else take away his pride and joy in starting a band