Disclaimer: I am not a financial adviser and you need to do your own research.
I won't repeat this good article on investing for effective altruists: https://80000hours.org/2015/10/common-investing-mistakes-in-the-effective-altruism-community/ . But one of the key ideas is if you are investing for yourself and you are young, or if you are investing for charity, temporary falls in value should not worry you. Taken even further, if there is a big payoff, but some chance of losing all your money, this can still be a good idea. This means that you are risk neutral, and just care about the expected (probability weighted) outcome. If you are like this, then I have an investment opportunity you may be interested in.
It is three times leveraged Russia. The Russian stock market has fallen precipitously, and it has fallen even more so from the US perspective because of currency changes. If it recovers to fair market value (mean reversion) over seven years, the value of your investment would be about four times as much. However, with three times leverage, even taking into account that you need to pay interest on the implicit loan, one would expect more like 50 times the money. Now there are impacts of volatility that I do not fully understand that could reduce this. But I have seen a 3X leverage produce 15 times as much money as the initial investment in 5 years and it was not quite as good an opportunity as Russia.
The downside of Russia is not just the normal potential for temporary loss of money. It is also possible that there could be a forced sell out of foreign assets, freezing of assets, or even seizing of assets, depending on international relations. So this is definitely not for the faint of heart.
But if you are risk neutral like I am, you may want to give it a try. The ticker is RUSL. I just put a significant fraction of my portfolio into it today.
Also, one could even argue that helping out Russia when it is worst off could prevent Russia from doing desperate things, so there may be global catastrophic risk benefits.
Update: March 17, 2016:
If you decided to invest when I did, congratulations - you have made 80% on your money in less than two months! This now means that the expected long-term return is significantly lower. Then when you include the volatility drag (see discussion below), it is not clear that this leveraged investment is better than just unleveraged Russia. So it might make sense to start phasing out of leveraged Russia and buying ERUS, especially if it is a large percent of your portfolio. On the other hand, if you think that oil price will continue rapidly reverting towards the long-term marginal cost of production, since Russia is highly correlated with oil price, you may want to stay in leveraged Russia longer.
Mean reversion plays generally have a timeline of years; I assumed that's what you were proposing. This should be obvious from the fact that you could have made the exact same mean reversion argument at the end of 2014 (2014's massive drops from the Ukraine crisis were when Russia arguably became undervalued according to your metrics), but actually RSX barely moved in 2015 as a whole. Sure if you cherry-pick the high in May 2015 you do well; hindsight-based cherry-picking always does well.
Over very short time frames (like <6 months), RUSS/RUSL are probably fine because there's limited opportunity for the transaction costs to build up. That is in fact what they are intended for; short-term bets. But if you're investing on the timeline of years, they're really bad, which is hopefully amply demonstrated by the (non-cherry-picked) data I gave for the last few calendar years.
Indeed, I did invest in non-leveraged Russia in 2014 because it was undervalued. But only now that it is extremely undervalued am I willing to make the bet on rapid upward movement where it makes sense to have leverage.