Forsaken has levels set up in a branching manner. If you beat level 1 in two minutes and 30 seconds or less, you'll go to the medium difficulty levels branch. Finish Level 1 in one minute and 40 seconds or less and you will go to the hard difficulty levels branch.

There are two other levels in which you can "warp" from the Medium path to the Hard path. They are "Catch the Orb" and "Power Down" -- (both found in the Medium path). In Catch the Orb, you'll have to chase down the third bounty hunter within the game (don't pick up the fake golden orb of matter) and once you destroy the hunter, he'll drop the real golden orb. Get it, and return to the starting point -- now you will be able to play the Hard path.

In Power Down, simply make your way to the end of the stage, (pick up a resnic reanimator -- extra life), hit all three switches, then destroy the enemies that come out of the now unlocked doors. Once this is done, the thing in the middle will lower it's protective armor, and then go to the front of it and blast the Red "eye".

(The other way to remain on the medium path, is to blast the eye at an angle while it's armor is still up.)