Bitcoin (BTC-USD) ends the year on the downslope, dipping 2.8% on the day to ~$45.9K and declining 17% for the month. For the year, though, the world's largest cryptocurrency gained 63%, outpacing the S&P 500 Index's 29% increase, showing no signs that its volatility will fade. It's a lackluster end to 2021 after reaching a record high of $68.8K on Nov. 10, according to CoinMarketCap. Checking in on how bitcoin-linked stocks fared for the month and the year: MicroStrategy (NASDAQ:MSTR) dropped 22% for the week and rose 45% for the year; Coinbase (NASDAQ:COIN) fell 8%; it's risen 1.4% the past six months (it only started trading in June); Bakkt (NYSE:BKKT) fell 43% in the past month and 12% for the year. For bitcoin miners, Marathon Digital (NASDAQ:MARA) slid 32% in December and jumped three-fold for the year; Riot Blockchain (NASDAQ:RIOT) sank 37% for the month and rose 38% for the year;