"Every cloud has a silver lining."

That's the old adage we use to remind ourselves to look for the positives in bad situations. It's a saying that investors might want to keep in mind these days.

There are plenty of clouds -- dark ones -- looming over the stock market right now. The S&P 500 and Nasdaq Composite Index are entrenched in bear markets. Many of the high-flying stocks of the last several years have plummeted. 

But there are silver linings to be found. Here are three stocks down 50% or more that are screaming bear-market buys.

1. Nvidia

Nvidia (NVDA 0.76%) ranks as the biggest company with shares down at least 50% so far this year. The stock has plunged nearly 60% below its high reached in late 2021.

The chipmaker's growth has practically ground to a halt. Nvidia reported that its fiscal 2023 second-quarter revenue increased only 3% year over year and fell 19% sequentially. The company's profits tumbled 72% year over year. But I think there are two main reasons to buy Nvidia stock hand over fist.

First, the company's headwinds are only temporary. NVidia faces supply chain problems and macroeconomic uncertainty that won't last forever. Nvidia CEO Jensen Huang said in August, "We are navigating our supply chain transitions in a challenging macro environment and we will get through this." I agree.

Second, the use of artificial intelligence (AI) will be increasingly used in data centers and autonomous vehicles. Nvidia is well-positioned to lead the way with the next generations of its graphics processing units (GPUs).

2. MongoDB

MongoDB (MDB -2.10%) has been hit especially hard this year, with its shares sinking more than 70%. But the database maker's stock has still delivered a gain of more than 5x over the past five years, showing just how high MongoDB soared before this year's sell-off.

Unlike Nvidia, though, MongoDB continues to deliver sizzling growth. In its fiscal 2023 Q2, the company reported that its revenue soared 53% year over year. It also easily beat Wall Street earnings estimates.

One problem for MongoDB is that its "earnings" remain losses at this point. Its bottom line is also moving in the wrong direction. The main culprit is stock-based compensation, which jumped 67% year over year in the latest quarter.

Still, the long-term trends definitely work in MongoDB's favor. More and more data continues to be generated. That data must be stored somewhere -- with the cloud as the top destination. When the stock market rebounds (which it will absolutely do sooner or later), I expect that MongoDB will return to its winning ways.

3. Medical Properties Trust

Nvidia and MongoDB will mainly appeal to growth-oriented investors. But is there a beaten-down stock that income investors would like? I think so. Medical Properties Trust's (MPW 4.61%) shares have fallen a little over 50% year to date. And there's a good case to be made that the stock is a screaming buy.

Medical Properties Trust is a real estate investment trust (REIT) that leases properties to hospital operators. Its dividend yield currently tops 10%. The company has increased its dividend for eight consecutive years.

The main knock against Medical Properties Trust is that many of its tenants face big challenges right now. Some hospital operators are struggling financially. One of the REIT's tenants even filed for bankruptcy recently.

However, Medical Properties Trust has successfully navigated similar difficult environments in the past. The company remains highly profitable with a solid financial position. Also, the outlook for its tenants should improve as their reimbursements increase in 2023.

I think now is a good time for income investors who aren't afraid of some volatility to lock in an exceptionally juicy yield with this stock.