Ambrosia

Ambrosia is the Dark God of Makai (Demon World) Amakusa and Mizuki were trying to revive.

Different Appearances

 * In Samurai Shodown (Amakusa's stage) Ambrosia had the form of an antropomorphic, winged and horned being with a skull in place of its face.
 * In Samurai Shodown II (Mizuki's stage) the Egg of Destroyer (a giant sphere with an infant child inside and eye symbol outside) located in the background seemingly represents Ambrosia.
 * In Samurai Shodown II, when Mizuki is defeated, we see Ambrosia disappearing in darkness, this time as a green fanged skull with purple glowing eyes and a symbol on its forehead.
 * In Shinsetsu Samurai Spirits: Bushidou Retsuden, Ambrosia has the form comparable to Elder God from Soul Reaver games or Zerg Overmind from StarCraft (in a sense of being a big mass of flesh), and the final battle takes place inside it.

Retcons, Backtracking and Controversies
There are also many specualtions about Yuga the Destroyer being Ambrosia, because:
 * they arguably fill the same spot in storyline (as mightiest villain/demon from Makai (Demon World), one of the most powerful beings that wants to invade and conquer the Human World, but cannot leave Makai)
 * they share the same eye symbol,
 * in Asura Zanmaden OVA, the cracking of the Egg of Destroyer was shown as a symbol of the coming of Yuga the Destroyer to the human world.
 * The Egg of Destroyer shows an infant inside it, and infants were the key point in the preparations to Yuga the Destroyer's invasion in the Human World.