The IT movie will place more emphasis on the traumas they’ve faced in real life and the mental scars left behind.
The IT movie certainly looks likea more horrific affair than the previous TV adaptation, so it’s fitting that the root of the fear comes from a more realistic source.
So even though his demonic clown guise is scary enough on its own, it’s how Pennywise can use those traumas to his advantage that makes him an indescribable terror.
In a way, that’s an improved approach considering that the It entity can manipulate a person’s deepest fears while preying on them with his shapeshifting abilities.