He didn't believe in the Siren and he was trying to make sure that the "Miss Tri-State Beauty Pageant" went down without a hitch. Otherwise, he would sell the property where it was held for a tidy profit.
She was determined to win the "Miss Tri-State Beauty Pageant" no matter what it took.
He was obviously wanting to do anything to make his client, Gloria Glamour, win the "Miss Tri-State Beauty Pageant".
Both stories thread the same needle. The keyword is beauty, kiddies. In the first story, a very shockingly drawn and fascinating faux monster stalks a pageant for motives all its own.
The method of the "monster's" attack acknowledges myth and inventively proves to be a soggy impediment for Mystery Inc. who look quite fit under the pencils, inks and colors of Williams, Davis and Becton. The consequences of the attacks allow for the subversion of Scooby-Doo formula without uncharacteristic action, and I can easily see the ending actually happening.