Attack mode

Attack mode (or sometimes called battle mode) is prominently an extra mode added to a Transformer toy to give ether or both robot and alternate mode a more combat orientated mode. It primaraly consists of a figure arranging or adding its weapons in a way so that it becomes more focused on combat then the standard robot or alternate mode. Sometimes it's uncovering weapons not seen on either mode. A good example of this is Ultra Magnus, by deploying his cannons on his back and fliping out his guns, he goes from imposing to "beating you to hell and back".

However, it can also be that the attack mode is a slight shift from the basic robot/alt mode, like folding wings onto their shoulders like Ransack or just pointing the beast mode head up on the chest as with Snarl. It is most likely that these modes are thought up by Hasbro to give the toy an extra bonus without actually investing in extra parts.