Early in the game, a group of soldiers can be seen lying dead in one of the surface caverns. This is the Galactic Federation Special Squadron that was sent to wipe out the Metroids, but were killed themselves. They are mentioned in the manual of Metroid II: Return of Samus (1991), but this is the first time that they are actually shown onscreen.
The first side-scrolling game in the series to include free aiming, a feature that was previously reserved only for the 3D Metroid Prime games.
New additions to gameplay in this remake of Metroid II: Return of Samus (1991) are: free aiming; the ability to perform a melee counter attack (similar to Metroid: Other M (2010)); the Morph Ball upgrade (which Samus had from the start in the original game); the appearance of the Charge Beam, Grapple Beam, Super Missiles, Gravity Suit, Power Bombs and the Power Bomb Cannon; Teleport Stations that allow for fast travel; Aeion Orbs that serve as fuel for four new suit abilities: Scan Pulse, Lightning Armor, Beam Burst and Phase Drift; and Chozo Seals that lower the purple acidic liquid and provide access to lower areas as soon as a quotum of Metroid DNA is inserted as proof of kill (in the original game, the liquid would inexplicably lower as soon as a certain number of Metroids were killed). Chozo Seals also act like a Metroid detector, showing a waypoint on the map near a place where a live Metroid can be found.
This is not the first remake of Metroid II: Return of Samus (1991) ever created. A fan-made remake called 'Another Metroid 2 Remake' (or AM2R) was released as a free download in August 2016, coinciding with the series' 30th anniversary. Although the game received excellent reviews, it was an unofficial remake and thus constituted a copyright violation, so Nintendo ordered all downloads removed. The official remake, Metroid: Samus Returns, was released a year later.