Paper Bowser is the paper counterpart of Bowser that appears in Mario & Luigi: Paper Jam and is one of the main antagonists of the game. Alongside various other paper characters, Paper Bowser came out of a book containing the whole paper world.
Mario & Luigi: Paper Jam
Paper Bowser makes his debut as a wholly unique character from Bowser in Mario & Luigi: Paper Jam. He first appears at Bowser's Castle, confronting the real Bowser and getting into a fight with him. Eventually, however, they decide to join forces and kidnap Peach and Paper Peach, subsequently returning to the castle and summoning Petey Piranha to slow Mario, Luigi, and Paper Mario down.
Eventually, the two Bowsers plot to betray the other and imprison them in the book, though not before they trap the Mario Bros. in the book and destroy it. The two merge together into Shiny RoboBowser, only to be defeated. Paper Bowser makes one last attempt to grab the book, but Paper Mario reaches it first, and the trio trap him back inside.
During their boss battle, the Bowser duo only has two attacks, both of which can deal considerable damage. Their first attack involves spitting fireballs at the ground, creating fiery waves for the trio to jump over. After three waves, they will combine their Fire Breath and create a massive fire blast that Paper Mario must jump over, or risk taking a large amount of critical damage. Their other attack is to have Shy Guys stack iron balls onto their hands. They will then toss the iron balls onto the field. The iron balls that target the trio varies depending on which Bowser tosses them last. The Bowsers will alternate between both attacks. Additionally, the Bowsers have a defensive ability: Whenever an Excellent hit is scored on one of them, they will curl up into their shells, forcing the other to be attacked. Due to this trait, only one Bowser can use the ability at a time. If attacked while in their shells, the Bowser will take no damage. Additionally, depending on the attack the trio used, that party member may also take damage.
The two Bowsers appear to share a health pool, unlike previous pairs of bosses. However, it is impossible to bring their health down to zero. After enough turns of battling, the Bowsers decide to stop holding back, and with the assistance of hundreds (if not thousands) of Shiny paper enemies, they fuse together into Shiny RoboBowser, the game's real final boss.
Super Smash Bros. Ultimate
He appears as two spirits in Super Smash Bros. Ultimate, one using his Mario & Luigi: Paper Jam artwork and another using his Paper Mario: Sticker Star artwork. The Mario & Luigi: Paper Jam Paper Bowser spirit can be enhanced to the Paper Mario: Sticker Star Paper Bowser spirit once it reaches level 99. Its class rises from Ace to Legend once done.