I recently reviewed Inti Creates' Azure Striker Gunvolt and gave it a solid thumbs up. The 3DS platformer is heavily inspired by Mega Man Zero and ZX, but it implements a unique combat system that involves tagging your enemies before shocking them with electricity. While the game itself is good, the best part is that every purchase comes with a free copy of Mighty Gunvolt, an NES-style demake that stars not only Gunvolt's titular hero but also Beck from the upcoming Mighty No. 9. Unfortunately, there has been no information on how to obtain Mighty Gunvolt by itself — until now.
Nintendo's eShop page for the title currently lists its release date as August 29, same as the main game, but mere hours ago that date read December 1. Since the promotion period to grab Mighty Gunvolt for free ends on November 28, that sounds like an appropriate time to release a standalone version. Once freely available, it'll be priced at a reasonable $3.99.
I personally think you should buy the two-for-one bundle while you still have the chance, but it's good that players will have the option to grab either game on their own. Also keep in mind that Inti Creates is planning to bring DLC to Mighty Gunvolt, possibly geared towards Mighty No. 9 content.