The core gameplay of Gradius Gaiden remains relatively unchanged. However, two new ships are made available whose weapon configurations are new to the series. Moreover, several changes were made on the weapons system. The chargeable E. Laser, the Reduce size shield, option types, are all items that have been removed in the transition from Gradius III: From Legend to Myth to this title. The player can select from four ships instead of a broad range of several weapon configurations like from Gradius III. Missile, Double, and Laser weapons can be additionally powered up one level, a feature from the MSX Gradius games (the powerup bar even resembles the one from the MSX games). These power-ups are permanent until the player is destroyed, even if he switches between the Double and Laser powerups. There are two new types of shield: 'Guard', which attaches to the top and bottom of the craft and renders the player immune to physical obstacle collisions; and 'Limit', which gives complete invulnerability and lasts for three seconds.
The difficulty level can also be adjusted from 'easiest' up to 'hardest', for a total of nine difficulty levels including the boss rush. On the easier difficulties, the more troublesome boss attacks are removed and the number of enemies on-screen is reduced.
At the near end of the eighth stage starting from the second loop of the game play, a Core Warship is added.
A player can rearrange the items in the power meter. This feature is only available in this edition in its series.
Jade Knight: Eponymously, every weapon this ship has is tinted green, including the options. Its missile, the spread bomb, is a carry-over from Gradius II: Gofer's Ambition. This ship has two different kinds of lasers available: round and pulse. The round laser, the most unusual weapon presented in this game, fires concentric rings of laser origination. The pulse laser is a two or three pronged burst laser, similar to the twin laser in previous titles.
Falchion β: This ship's weapons are variations on well known themes. The Falchion has a two way missile called a rolling missile, which tumbles to the ground where it splits and shoots both left and right. It also has a three-way limited range shot called Auto-Aiming, that fires a second shot within the angles of 0 to 180. Its laser weapon is the gravity bullet, which is a newcomer to the Gradius series but is present in several earlier Parodius titles. It is based on the Spread Gun that is yielded by Pentarou in Parodius Da! and every title afterward.
Also, it has been speculated that the ship is not new at all, but an upgrade of the Falchion from the 1987 Konami game of the same name.
Source: Wikipedia, "Gradius Gaiden", available under the CC-BY-SA License.