here is a guide and my first one to earn a Gold medal in all challenges.
Rooftop massacre=Go to the underground lab and pick up 2 blast frequenzy guns and create 2 Super B.F.G.s(Blast frequenzy gun+Amplifier). Start the challenge and you get a lot more than 40 kills.
Silver strip smackdown=Pick up the 3 combat magazines(combat 1= Silver strip at luaii wauwii; combat 2=In the Palisades mall at Stan's Large Print Books and Mags; combat 3=In the left upper corner off the Slot Ranch casino). Now you create a Boomstick(pitchfork+shotgun; both weapons can be found at the southside of the Palisades Mall). Start the challenge and kill the zombies by hold the X button. If your out of ammo use another gun but the boomstick is enough.
Ballon man=At the start the stairs are full of zombies but one shoot with the super B.F.G. clear it. Run up and shoot again. Run around the left corner and you see a phone cell. Climp up the phone cell and on the roof. There you can shoot two more times to clear the way.
Crowd Pleaser=Stay in the front of the stage and press&hold Left on the Dpad. Do this the wohle challenge and all zombies come to you.
Chop Suey=Create a Plate Launcher(Cement saw+Plates) and shoot into a huge zombiehorde. It's very easy in my opinion.
Rumble in the Jungle=(The same as Rooftop Massacre)
Stiff Back=To difficult to explain. Watch the Video.
Killing Floor=(The same as Silverstrip Smackdown)
Murder on High Seas=(The same as Rooftop Massacre)
Rule #1=Before start the challenge pick up the Drink cart in Bennie Jack's BBQ Shack and put it near the challenge star. Now start go to the Drink cart and Push it, with the cart you are faster. In the BBQ Restaurante run up the stairs and jump over the lights. Ignore the Zombies on the Stairs. The Zombies on the lights are jumping down before you reached them.
Do not try this at Home=(The same as Silver Strip Smackdown)
Thirst Quencher=Before ypu start, pick up the Drinking Magazine(Found at the end of the challenge Rule #1). Now start it and cancel it. Now fill you Inventory with alcoholic Drinks(put your old Inventory anywhere where you can find it, except the Magazine). After all that you start the challenge and run into the Poker room on the left side. Drink all your drinks, pick up the others in the room and drink them too. After this you should have 18-22 Drinks. Now go outside the room to the Bar and drink the other Drinks.
Ijiek Motors Presents...=To easy to be a challenge. Use the bike and drive up the strip. Without crashes!
Party Hard=First you need the Caddy near the challenge. Drive to the star and start. Now get in the Caddy and drive back to the Line and hold Y the whole challenge. Drive back and forward. If enough Zombies are near the line stay at the star.
Extreme Off Road=Use the chainsawbike. Chainsaw can be found on the stage. Climb up the big Speakers.
Scaffolding Shuffle=I use the skateboard+Skateboard Magazine(can be found in the Ultimate Playhouse; Palisades Mall).
Drive with your skateboard through the Zombies and climb up the statue on the left side.
Killer Rides=Before started, pick up the Metal Barricades around the Rocket Ride and don't kill to much Zombies. After that start the challenge. go to the place where the Rocket swings and press&hold Left on the Dpad. watch at the Rocket. If you see it will come back roll to the side. Rocket way= 1-halfway back; 2-forward 3/4 up; 3-Fast back and stay at the top for 4-5 sec.. I used the celebrate move between step 1-2 and 2-3 with a risk. At step 3 you have the best timing to do this. after that the Ride is to fast to celebrate.
Fast Food=Buy the Sport car in the Royal Flush Plaza and drive to the challenge. Start and drive as fast as you can up. At Lombardie's there are 2 Snack machines. climp them up on the roof and follow the way.
Shutter Bug=I used the Sniper rifle. Look to the Zombies and shoot some Zombies near to you. Now press as fast as you can RB to go into the Photo mode and take a Photo. You get a lot of Horror(1-10 Points) and Brutality(80-300 Points).
Pawned Prestige=(The same as Silver Strip Smackdown)
Robot Race=Use the Bike found at the Silver Strip. Start the challenge and drive to Lombardie's. Near this Shop is a Space house or whatever. Go up the stairs and jump out the Window. Run to the left and jump up to the Roof.
Burn the Bodies=Best is to use 2 Flamethrowers(Watergun+Gasoline Canister). Run into a Zombiehorde and burn them all down. Very easy to beat.
Lightning never strikes twice=The only way to beat this challenge is to use the Tesla Ball(Bingo ball+Battery). You will need 2 of them. I buy 2 at the Pawnshop on the Silverstrip. Put one Ball near the star and the other is for you to use. keep sure the other ball is there, sometimes the other Ball will spawned away. Start and throw the Ball into huge Zombiehordes. you will kill between 80-100 with one Ball and you got 2 of them.
Tunnel Vision=Use a Bike and drive to the left, follow the Tunnel you can't miss the Goal.
Mad about Hats=pick up a lot of Lizard masks and put them into the Giant craps Table. It's better to have over 20 hats on the field and have your Inventory full of them. Start and put masks on Zombies heads, pick up the others and do the same. Don't stop if you have 25, sometimes a Zombie loses his mask.
No thanks, I'll Stand...=Watch the Video.
Tunnel of Blood=Use the chainsawbike and drive through the whole Tunnel.
One Armed Bandit=Keep sure you have both gambling magazines(First one-In the Palisades Mall near the Water slide on a Table; Second one-In Bennie Jack's BBQ shack on the second floor). Now start the challenge and go to the Big Slotmachine to the Right and press the Right Button. It's more Luck to beat it.
Double Trouble=Keep sure your Life is full. I use the Lasersword and right after the countdown end drink a Quick step(Wine+Wine; in the Baron von Brathaus Restaurant). To attack both, only one. If you failed reload the last checkpoint.
Rooftop Massacre: Round 2=(The same as Rooftop Massacre)
I hope it helps and sorry for my bad english^^