Barbariccia, Draghignazzo, and Malacoda are members of the Malebranche from the Inferno. It's possible that final area is also intended to be an Inferno reference, especially given that it has multiple segments with different themes, one of which is frozen.
Zephyr shows up to reference everything else about Dio that Soma missed.
Several bosses utilize mirrors to escape Soma's attack, forcing him to manipulate their reflections to make them vunerable.
Popeye of all things gets one too. There is a usable healing item called Tinned Spinach and the description reads as "May give the illusion of bulking up muscle mass." Sadly, it neither heals you very much nor gives you a temporary boost in attack power.
It may or may not have been intentional, but Menace's "antibodies" are remarkably similar to The Langoliers.
It seems more than just coincidence that the enemy clowns sometimes drop hamburgers when killed.
