Here is the full list of all 8 Unreal Development Kit achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Have 60 seconds of "UDamage Time".
Play a match with every mutator, using only 1 per match.
Get the "Roadkill" award 4 times.
Get 4 kills with the Shock Rifle.
Get 4 kills with the Rocket Launcher.
Get the "Killing Spree" award.
Get 4 kills with the Link Gun.
Get the "First Blood" award.