This is my general guide to the non-DLC Dungeon Defenders challenges. I will be giving some general tips on how to beat these challenges, as well as specific tips for specific challenges
I must point out that this is not a guide to doing these challenges on Insane or Nightmare difficulty, nor is it a guide to soloing these challenges. This is a general guide with tips that apply to each challenge, regardless of the difficulty.
The Two Laws of Challenges
If you are trying to do these or any other challenges, whether on Easy or on Nightmare Hardcore, there are two laws that are always true:
A higher level makes challenges easier.
The higher level you are, the easier it will be for you to complete the challenge. Depending on the challenge and difficulty, if one character is level 70, and the rest are level 10, the level 70 character can do all of the work while the level 10 characters sit around and encourage the level 70 character.
More people makes challenges easier.
The more people you have, the easier a challenge will be. 4 level 70 characters will have a much easier time completing a challenge than 1 level 70 character will.
Now, onto the challenges!
Challenge 1: No Towers Allowed
This is the simplest challenge out of all the challenges. The safest way to beat this is to have 4 people each guarding one of the 4 entrances to the crystal. Huntresses and Rangers are especially valuable on this level, because their range makes it much easier to kill the minions without missing any. One thing to note, however: don't starting going on a rampage up to the spawn points. You may miss a mob and give them a free trip to the crystal. This is an easy and straightforward challenge if you play smart.
Challenge 2: Unlikely Allies
This challenge is easy, but can be irritating due to the friendly ogre. The ogre likes to engage the minions, so putting defenses near the spawn points, as opposed to the more traditional setup at the three main choke points near the crystal, will prevent the ogre from getting swarmed and dying. Because the ogre will push your blockades around, I recommend putting harpoons or any apprentice towers overlooking the spawn points. When the ogres spawn on the last 2 waves, you need to kill them as quickly as possible. The ultimate goal here is to keep the ogre away from combat, and easiest way to do that is to kill all the minions before the ogre gets there.
Challenge 3: Warping Core
This challenge requires some work. Because of where the core will warp to, placing defenses in the traditional manner at the three main choke points is inadequate. You must place defenses closer to the spawns. The other thing you must do is stay near the core. The core is more vulnerable than usual when it warps, especially when it warps to the lower levels, because it's easier for mobs to get to the core. Stay with the core wherever it goes.
Challenge 4: Raining Goblins
This challenge is a lot easier than it looks. All you need to do is place defenses all around the crystal. Bouncer blockades are recommended. Just remember to repair your defenses and kill those that drop near the crystal, and this challenge will be easy for you.
Challenge 5: Wizardry
This challenge is so much easier if you have 4 people. When you have 4 people stationed around the map, each covering different spawn points, it's much easier to kill the vulnerable mages and finish the level because you don't have to run around the entire map by yourself.
Challenge 6: Ogre Crush
This challenge is a lot easier if you have 4 people, although it's possible to do it by yourself. The main point of difficulty is that your defenses cannot kill the ogres by themselves unless you have amazing stats. If your defenses are tough enough, you can run to each ogre and kill them yourself before they destroy your defenses. But it's a lot easier if you have 4 people.
Challenge 7: Zippy Terror
Zippy Terror is almost impossible to do by yourself. Even with 4 people, it can be difficult, especially since you can't place any towers. I recommend having multiple Huntresses or Rangers and pets that can do enough damage to kill a kobold in one shot. Kobolds on insane have about 1000 health.
Challenge 8: Chicken
This challenge is not that difficult if you coordinate with your teammates. Fortunately, a traditional setup will work here, although I recommend that you place your defenses closer to the spawn points. Along with killing the creatures that spawn, you must also protect the Chicken, who moves slow, cannot jump and dies with one hit. Dark Elf Warriors and Wyverns if you can't kill them easily are your greatest threat. I recommend that the Chicken stand behind one of the crystals. Remember that the Chicken has a limited number of lives, and the status of Chicken will switch occasionally. (Note that when doing this challenge by yourself, you will not be the Chicken for the entire time. You will switch between being the Chicken and not being the Chicken.) As long as your defenses can handle the waves and you can protect the Chicken, this challenge shouldn't be too hard.
Challenge 9: Moving Core
This challenge is similar to Warping Core. Like Warping Core, it is better to place your defenses near the spawn points. There is only one crystal on this map, and that is the central crystal in the traditional Royal Gardens map. It starts by moving to the left and up the stairs, then moves around and goes down the opposite set of stairs. You should have one person stand on top of the crystal as a final line of defense. One thing to note is that the crystal stops moving once the wave is cleared. Furthermore, the crystal doesn't move very fast, so as long as you clear the waves fast, you can stop the crystal before it goes down the opposite set of stairs and into a harder-to-defend position.
Challenge 10: Death from Above
This challenge isn't very hard as long as you have good defenses. If you don't, however, it will be a challenge and will require good coordination. The only minions that spawn on this map are wyverns (including mini-wyverns and super-wyverns) as well as ogres. Huntresses/Rangers are especially effective on this challenge. If your towers can kill all the wyverns without your help, then it's easier to focus your attention on killing the ogres, which makes the level much easier.
Challenge 11: Assault
DPS heroes are almost required for this challenge. Huntresses and Rangers are incredibly useful on this level, despite the fact that the range on ranged attacks are severely reduced. But as long as you have a DPS hero, you should be able to do this level. You won't be able to complete this challenge by yourself if your hero is specializing in towers.
Challenge 12: Treasure Hunt
This challenge can be difficult, but if you have defenses that don't need to be frequently repaired, then this should be straightforward. Each wave will spawn endlessly until you grab the necessary amount of gold tokens. Gold tokens drop from certain enemies and only last for 5 seconds. Fortunately, enemies that drop gold tokens are completely golden, as if they were buffed by a Djinn. You need to hunt down these golden enemies and take the token. In the later waves, 2 ogres will spawn frequently at the lower gates, so be aware and take them down before they destroy your defenses.
Challenge 13: Monster Hunt
This is the most difficult non-DLC challenge. Which makes sense, since Glitterhelm Caverns is the most difficult non-DLC level. Like most of the other challenges, your defenses should be close to the spawn points, which in the case of Glitterhelm, are usually close to the spawn points anyways. However, you must help kill the creatures faster than the defenses can kill them alone if you want to beat the time, and it is especially important to focus down the ogres fast, as they will tear through your defenses and make it harder to finish the wave on time. I recommend having 4 people stationed around the map like I recommend for the Wizardry challenge.
I hope this guide was helpful to you. Like I previously said, this guide is for the non-DLC challenges on any difficulty. While this guide does not give many specifics, it should at least help you to not feel intimidated when you do one of these challenges.
Anyways, so long Heroes!