Rage mode will be unlocked while going through the level with Electro. You can only use this on the Ultimate Spider-Man, which is the black symbiot suit. This doesn't have to be for a minute straight, it's just a minute total that you have had this active. It still saves your time, even if you have died. You should be able to easily get this in the level you obtain the power. The bar will not automatically fill up. You must engage in combat to build it. The bar is blue and located under your health. Start it only when it's full by pressing . There are upgrades in the menu associated with this power as well.