Valak is a giant dick. But we suppose you don't become president of Hell because someone forgot to baptize you. Besides shoving couches, he orchestrates one of the most chilling massacres in U.S. history, the Amityville murders. So viewers probably expected him to be a formidable opponent. And sure enough, the two paranormal investigators who go up against him looked seriously outmatched. They're taking on a metaphysical monster without a single nuclear accelerator on their backs.
The Weirdly Easy Solution:
Valak has one very stupid weakness: his name. If you speak his name, he is banished back to Hell. This raises a few questions. Why should this work? Does it work if you scream his Twitter handle? Can you give him a nickname and then scream it? All we know is that a demon should probably never tell anyone his name for any reason. Which, unfortunately, Valak does at the very first opportunity.
Warner Bros. Pictures
This idiot demon, who obviously didn't read even the first page of his haunting manual, can't help but answer the protagonist's question "Who are you?!" by yelling his name out loud. The exchange occurs within a chilling dream sequence, so it's possible that Valak, Lord of Terror, got overexcited and dropped the ball. Either way, you'd expect a conniving archdemon to have a little more sense.
The protagonist later recites the name and promptly brings Valak's antics to an end. This is at the point when Valak has moved from interior decoration to full-on demolition, tearing the haunted house asunder and endangering its inhabitants. But within moments of his name being called out, the reign of terror ends. The dumber-than-dumb demon is defeated and the movie gets a happy ending. We're maybe not in a position to make fun of someone for who they elect president, but nice work, Hell. Your president sucks.