MDK is a third-person shooter game developed by Shiny Entertainment and released in 1997 by Playmates Interactive Entertainment for the PC, Macintosh, and subsequently PlayStation. It was one of the first games to run only in Pentium or superior range of processors (for the PC version) but did not have a GPU requirement. The game soundtrack, composed by Tommy Tallarico, was also released.

The game tells the story of its protagonist, Kurt Hectic and his attempts to rescue Earth from an alien invasion of gigantic strip mining city-vehicles named 'Minecrawlers', which are not only removing all of earth's natural resources but are also flattening any people and cities that get in their way. The game combined fast action with fully 3D rendered, state-of-the art (for the time) graphics and a warped sense of humour. It featured a "sniper mode" that allowed the player to zoom in on an enemy targets. (Wikipedia)

Codes

Misc. Codes
Pause the game and press L1, Up, Square. Unpause, pause again and press Square, Triangle, L1, L1, Left, Square, Triangle, Circle, Right, L1 - 150 Hit Points and Extras

Pause the game and press L1, Up, Square. Unpause, then pause again and press Triangle, Right, Circle, Left, Left, Circle, Triangle, Triangle, L1, Right - Bones Airstrike

Pause the game and press L1, Up, Square. Unpause, then pause again and press Down, Down, Triangle, Triangle, L1, X, Triangle - Display Coordinates

Pause the game and press L1, Up, Square. Unpause, then pause again and press X, L1, Right, Circle, X, Up, Square - Dummy Decoy

Pause the game and press L1, Up, Square. Unpause, then pause again and press Up, Down, Down, L1, Right - Earthworm Cow Power Up

Pause the game and press L1, Up, Square. Unpause, pause again and press Down, Up, Circle, Down, Up, Down, L1 - Extra Airstrike

Pause the game and press L1, Up, Square. Unpause, then pause again and press Right, Circle, Triangle, Circle, X - Faster Speed (press R2 in game)

The opening video of this great game: