I honestly think it would still drop. The Nintendo investors have shown time and again they've got zero concept of the market, be it video games or stocks. I can't think of a time their stock has stayed neutral or even risen after any announcement whatsoever. 

Nintendo venturing into the mobile market is what caused their stocks to rise to the previous level so it makes sense that any mishaps will have a negative effect.

The "game" announced (Miitomo) is not even a game (a Mii app, yeah...), so the reaction is understandable, and even healthy IMO. You can't praise something like that...

Considering they keep delaying everything, is normal that investors are unhappy. I mean, that must be a very very patient people to keep giving them more opportunities.

Hopefully this resonates high in the HQ and start working in a more effective way.

I doubt it.

Remember when Ubi's stock plummeted 26% when they announced that Watchdogs was delayed and would therefore miss out being a launch title PS4 and XB1? With so many short memories around here, I wouldn't bet that many do. As it was, that turned out to be just a blip in the grand scheme of things.

Granted, this was a sudden drop, but Nintendo stock  was lower on Sept 29th, and also through parts of June and July. We'll have to wait and see what happens in the next few days.

Maybe it's time to make some new investments. Nintendo is a popular brand. It could grow into new markets.

Taking longer than expected and it's not the franchise investors wanted (Mario).

Is at -8.9% now, it is slowly recovering, same with Dena, that is at -14.9%

The real reason

This happened because investors were expevting a release before years end and also a mario/zelda/metroid(a Nintendo IP) game, instead of this game using mii and being more of a social app