Mechagodzilla, also referred to as Kiryu, is a reference to the 2002 and 2003 films Godzilla Against Mechagodzilla and Godzilla: Tokyo S.O.S. This is the mech that Nolan Sorrento pilots in the Battle of Castle Anorak. This mech is near indestructible and has a powerful lightning attack, but this is countered by its slow speed and maneuverability.
It made an appearance in the final battle, used by Sorrento to fight against the Iron Giant. The Kiryu design, however, is not used. Instead, a new version was created, apparently modeled after Legendary Goji from Legendary Pictures's 2014 film "Godzilla".