Scarier means more frightening. Scarier than the first, gets scarier, scarier still.
It is the comparative of scary, and the y turns to i before the ending, as it does in happier and easier. Scary is informal — frightening and alarming are the neutral words — which is why scarier suits films and stories rather than official warnings. Note scariest; and that scare has been a verb since Middle English.
1adjectivescarierMore frightening.
“The second film was even scarier than the first, and I watched it through my fingers.”
scarier is a comparison of fear.
scary comes from scare + -y.
Etymology from Wiktionary, CC BY-SA