Giant-Man is based on his appearance in Captain America: Civil War. Unlike most minifigures, he is completely brick-built. He is also bigger to scale with an ordinary minifigure.
Giant-Man is the result of Ant-Man's use of Pym Particles to grow rather than shrink. Unlike when he is small, Giant-Man has strength proportional to his size.
He appeared in Captain America: Civil War, on Captain America's team.