Bowser Jr. 64 is a hypothetical title. There is no officially released Nintendo 64 game with this exact name. The title suggests a game potentially featuring Bowser Jr. as the main character in a platforming or adventure setting, taking advantage of the Nintendo 64's capabilities in 3D graphics and gameplay.  The game, if it existed, likely would have involved exploring worlds, solving puzzles, and engaging in action-oriented gameplay elements.  Its hypothetical nature means it's impossible to provide details on developer or specific gameplay features.

Bowser Jr 64

Bomberman Hero (USA)