"Goldd, Wu-Lord of Dark World" and "Sillva, Warlord of Dark World" are based on the two antagonists featured in the Japanese Television Series Monkey Magic called Kin-Koku and Gin-Koku (Translated, Gold Horn and Silver Horn), who were Kings of the Underworld.
Their names might as well be based on two important pieces in the Japanese chess game, Shogi, the Gold and Silver Generals.
Sillva is the "Dark World" color pun meaning Silver.
This card's Chinese name, 銀魯巴, is a combination of 銀 ("silver") and 魯巴 lǔbā (transcription/transliteration of ルバ ruba as in its Japanese name シルバShiruba).
In alchemy and economics, silver is considered valuable, though inferior to gold. It is interesting to note that Sillva has similar stats to Goldd and a similar, though arguably slightly inferior, effect. Their titles, Wu-Lord and Warlord, also sound similar. To further is hierarchy, Sillva is only a common in the gold series, while the coincidentally named Goldd is a Gold Ultra Rare.
This could be an explanation for the design of this monster and "Goldd": The head of this monster consist of two skullfaces. The first can be viewed normal and the second on his forehead(rotated by 180° and using the same eyes). In contrast to "Goldd, Wu-Lord of Dark World" which head have 3 skullfaces (one big and 2 small faces rotated by 180° on the sides). The same applies to the orbs on the chest on both monsters ("Sillva" have 2 and "Goldd" have 3).
Wu "武" in Japanese/Chinese means forces or kongfu. Respectively, Sillva's Japanese name is the god of army, and Goldd's Japanese name is the god of forces.
According to Master Guide 2, "Sillva" and "Goldd" are the heads of the Dark World's military and serve beneath "Reign-Beaux," the political and religious authority, and "Sillva" is in fact the senior partner of the two. The two are in turn immediate superiors to "Brron," though this was portrayed in the exact opposite way in the anime.