This is Gaur Plain, from Xenoblade Chronicles. It is a huge field located on Bionis’ Leg. Shulk and his friend, Reyn, traveled here to reach Bionis’ head following the Mechonis’ assault on Colony 6.
In Smash Bros., the stage has two long platforms on either side, with smaller ones underneath suspended above a gaping pit. This stage undergoes a day/night cycle, and features the god Mechonis in the background. At nighttime, Metal Face flies in from the background as a boss. He'll slash with his huge claws and fire a laser to destroy one of the two large platforms on the stage. Unlike in Xenoblade Chronicles, any fighter can harm Metal Face's armor. Fight back and defeat him!
Note: You can play on this stage and its Ω Version in 8-Player Smash.