Narcomoeba was first printed as a "Future card" in Future Sight, with the special card border. It was reprinted in the original Modern Masters, at uncommon. That was 3 years ago.
This price movement is due to supply finally drying up to steady and perennial demand in Modern and Legacy combo decks.
The Future Sight foils did not take much of a hit from the reprint, still sit at $7 or so, and are about to jump to $12-$15 in the next couple of months. Lower yield and higher outlay makes me focus on the MM foils, instead.
Modern Masters foils are percolating over $3, and likely will jump to either $5 or $10 within the next couple of months. Non-Foils are passing $1.50 each now, and will likely spike to $5 before settling around $4. I'm most bullish on Modern Masters foils.
The emerging market price for Naromoeba will be at a plateau higher than before the reprint, due to the explosive growth of Modern in the last 3 years.
Expect to see Narcomoeba reprinted within a year or two, so stay nimble on these. But until we see a reprint, expect step-wise growth.