Gradius Gaiden's Final Boss, called "O.V.U.M", is Bacterion who has become Giygas.Just before you fight O.V.U.M, you see a red image in the background before the background changes. That is Bacterion in his "Giygas" form. After the background changes, 3 Intruders (the dragon boss from Salamander) fly from the background into the foreground to form Zelos, which change into Brain Golem, which changes into a small sphere that can be destroyed. So Bacterion materialized himself to battle you, which didn't work.
Vic Viper doesn't get destroyed when it gets hit/crashes into somethingThe temporal space fighter is simply equipped with some sort of proximity-triggered failsafe that warps it away to a previous safe spot before it is destroyed or serious damage is done, the trade-off being a high energy cost (lives and power-ups). This would explain the Vic viper's memetically fragile nature, as well as why the explosion looks like the ship zapped out of existence.
Gradius V Stage 1's boss is being piloted by the moai, or the spirits thereof. Furthermore, the moai were driven to extinction.It would explain why said boss shoots rings that can be shot away, and why V does not have a moai stage.
Gradius V and Gradius NEO are Continuity Reboot of the franchise.Since Gradius V is set in the same millennium as Gradius NEO (both set thousands of years after previous Gradius games) It would be safe to assume that the Gradian Empire doesn't even exist anymore prior to the events of Gradius V. Also, the Lars Empire is behind the Bacterians who was destroyed in Gradius V. WMG.Castlevania) is obviously an alien. Galamoth didn't appear till 1796 (7807 Gradius year) and Red Falcon didn't appear till 2633 (8644) and Black Viper two years later, both well after Gradius IV, where Gofer broke himself into pieces. Some of the pieces could have landed on Earth as Galamoth and later Red Falcon and Black Viper.