Stack-Up (also known as Robot Block and simply Block (ブロック Burokku) in Japan) is a video game released in 1985 for the Nintendo Entertainment System, designed for use with R.O.B. the Robotic Operating Buddy. Stack-Up is one of two games in Nintendo's Robot Series, the other being Gyromite (Robot Gyro in Japan). While Gyromite is a pack-in game with the R.O.B. itself and therefore comes with all the parts needed to play the game, Stack-Up comes in a large box containing additional bases and colored discs. The game's retail box comes with many small, plastic parts, which may contribute to difficulty in maintaining a complete set. Stack-Up is considered by collectors to be one of the rarest first-party games for the NES.