Assembloids 2600 is a fast paced reaction puzzler based on the 2010 game Quartet. The playfield consists of 5 windows, arranged in a plus shape. Parts of creatures in different colours appear in the central one, and then have to be moved to one of the four other windows using the joystick. If a window already has the space of that part occupied the player will lose a life. A life is also lost if the player takes too long to move the part. When a full creature is assembled the player is awarded points. The more uniformly coloured the creature is the higher the point gain. If the player manages to clear all the windows and extra life is awarded.
The game gets faster as it goes on, losing a life will slow it down a bit, but upon doing well again it goes back to getting faster pretty quick. There are a number of difficulty settings available, which have an impact on how fast the game gets and how quickly the speed picks up.