Billionaire investor Warren Buffett is doubling down on his bitcoin criticism.

"Bitcoin has no unique value at all," Buffett told CNBC's Becky Quick in a "Squawk Box" interview Monday. "It is a delusion, basically."

The Berkshire Hathaway CEO said he is sympathetic to optimists who bought the world's largest cryptocurrency in hopes that "it would change their lives." Bitcoin has lost more than 80 percent of its value since reaching a high near $20,000 at the end of 2017. The cryptocurrency was trading near $3,781 on Monday, according to CoinDesk.

"It attracts charlatans," Buffett said. "If you do something phony by going out and selling yo-yos or something, there's no money in it — but when you get into Wall Street, there's huge money."