Compared to Ultra Super Saiyan strength doesn't increases that much, but speed is increased multiple times. and the hairs of a Super Saiyan 2 are more split and spikier. Super Saiyan 2 was achieved by Gohan against Cell when he destroyed Android #16 by standing on his head and crushing the life out of him.
The ones who achieved this goal are: Goku, Vegeta, Gohan