You know, like some Disney characters do. It’s still possible that he’s able to use some magic trick to make everything gigantic in a specific situation and in a restricted space, as if he creates a “dimensional sphere” around him while he’s doing something specific (like playing).

Unless he’s able to change the size of the entire casino AND his own body size, I’d say that he’s probably able to use his magic to make you smaller (that would explain why Cuphead/Mugman looks so tiny in the pool table). Speaking of King Dice-Game, he also looks gigantic when you fight against him, but it looks more like a magic trick since everything become bigger around the player. We don’t know if the real size is the “normal one” or the “gigantic one” (maybe he likes to stay tynier so he can live between “humans”, or maybe he uses his magic to increase his size, or maybe Devil-Show real size is the gigantic one since he has a giga-fork as trident). So… When at “normal” size, Devil-Game looks bigger than Devil-Show, but when they increase their size, then giganticDevil-Show looks bigger than giganticDevil-Game. We know that (according to what the creators have said) the show isn’t exactly in canon with the game, so we can only speculate, but I can see a pattern between the Devil-Game and the Devil-Show, since Devil-Show can change his body size too and he can become gigantic too (maybe even bigger than Devil in Game).

In game, he looks way bigger when sitting on his throne, not to mention he becomes gigantic in the 2nd and 3rd phase in the last fight. I’m not sure if his real size is the one he generally shows to people. One important thing: Speaking of the Devil, I think that it will remain a speculation since apparently he’s able to change his body size. I can create a visual high comparison to clarify why I came to this conclusion, if you like! My impression is that the Devil-Game is TALLER than King Dice-Game, which means that he’s also taller than Dice and Devil-show (because Devil-Show looks a bit lower than Dice-Show). I have a couple of images as reference to understand heigh difference between TheDevil-Game and KingDice-Game, so I think it’s possible to estimate a comparison between Devil-Game and Dice-Show. King Dice Show how much lower than the Devil Game?

Cuphead king dice battle drawing