Dennis started out as a Christmas mascot: A gorilla with an Angryfaic for a head who threw mince pies.
Paladox then decided to make Dennis the Boss of The Game. He stayed true to being an angry gorilla who threw mince pies. This is the first time Dennis has actually been called by his name. As the player gets closer to defeating Dennis, the Angryfaic turns from yellow to orange to red. When it is red, he will fire a lazor. This catches many players out after how easy the Boss fight is prior to this attack.
Dennis then appeared in a presentation that Paladox had to do about Japan. After a few images of real things that actually exist in Japan, Dennis was seen throwing mince pies, but with text appearing shouting at Dennis that he's supposed to be throwing rice cakes.
Dennis is always throwing mince pies, since when he was created, his job was a mince pie throwing mascot.
Dennis' name actually comes from the Internet Meme "MY NAME'S NOT DENNIS!"
Dennis' lazor in The Game doesn't appear to be a real lazor, or at least isn't the same type of lazor as the others. It is yellow and triangular, and it solidifies and rotates.