Most of these "challenges" sound like achievements/trophies...
Skynet challengeYou play an operative and must hack several placed turrets around the map, you have a time limit depending on the difficulty level, on easy it is 10 minutes, on medium it is 7:30 minutes and on hard it is 5 minutes. Also, the difficulty changes the number of Engineers and Operatives on the opposite team, there are always 5 engineers and the difficulty adds +1 operative who will spot you, and give away your position to the turrets.
Anti-Gravity impaired You play a light of any class, you cannot jump or preform parkour, you must run through a time trial map, however there is heavies with GL running around, which will knock you down and make you lose time having to get up. You cannot die, and the heavies have a slow reload time. On easy, there is a single heavy, on medium there are two, on hard there are three without a reload penalty. The time to get to the end is the same on all time difficulties.
FRAG OUT!A practice mode challenge, you get infinite grenades, no cooldown, and you must hit enemies as they run by. You get 5 minutes to set a highscore, lights are 5 points, mediums are 20 points, and heavies are 50 points, but the points are only rewarded for KILLING them knocking them down will score few points but will give you the chance to kill the downed enemy.
Lazarus out!A kind of versus challenge, its two players, one plays a medic and must prevent kills, and the other will play a soldier with a GL and grenades, (both players get unlimited grenades and no cooldown.). The players will switch sides after the 5 minutes time limit, the player with the higher amount of points (from kills, rez give you no points) wins the match. Both players are competing to get a high score for each difficulty.
Oh and btw Deathshroud made a Duck Hunt reference.
EDIT: ...ninja'd, or is it Wraith'd around here?