Mymx is worth so little that the tax loss is worth far more than the stock if you owned it since the spinoff. It is a highly speculative stock which will most likely become worthless. There is a small posibility of big payoff if some of their drug research is bought by a major drug firm. Without revenue, or reasonable prospects for revenue in near future, there is no way to perform any reasonable valuation.
Bottom line: IMHO, sell if you need a tax loss this year. Otherwise, it is relatively illiquid. Selling would result in a major commission if small shareholder and major price drop if a large holder. Since the value of my MYMX shares is so miniscule, I have chosen to hold for now.
You won't get much of a tax-loss break on the sale of MYMX. In fact, you'll have to pay taxes on gain. The distribution was to be treated as a dividend with no adjustment to the value of MXBIF stock. The cost basis for MYMX shares was $0.02542 (Can$0.04). So given the $0.27 price today - you'll be paying taxes.