There are 5 hidden "Sega!" voices in the Japanese version of the game, featuring an alternative Antowas voice, Astal, Geist, Gerardo and Leda.
Astal's spine did not feature the game's name, which may have lead to its poor sales in the US. Retailers would have had to display the case forward facing, rather than to its side as standard.
There's an unused sprite in the game's data of what appears to be Mario, though the sprite's palette is more in line with that of his original outfit of red dungarees with a blue shirt.