Why Have Zombies Evolved Again?

[Apocalypse + System + Mecha + Zombie + Evolution] Hell is full and the dead return to earth. Zombie cans fall from the sky, and those who inhale the green mist from the cans turn into zombies, and the world enters the doomsday era. Li Tianyang traveled through time and came to this parallel world. Fortunately, he had a mechanic system. "Did this system come to the wrong place? It's just fighting zombies. Why did it directly activate the mecha for me?" "... Wait a minute, you call this mountain of flesh more than 100 meters high a zombie?!"