Tomb will most likely be the first challenge you find yourself grinding. It drops The First Flame which will become The True Flame on its final evolution, a DPS-oriented item that’ll offer a great deal of armor penetration and additional damage. Most DPS, healers, and even tanks will use this item in most situations for its substantial damage output and ease of use. Fortunately, all challenge items are unique in their own right, meaning that you can replace any item you want for a challenge drop. However, be aware that you can only possess a single challenge item on your hero at a time. More can be stashed. 

Drops: The True First Flame and the Spark Of Creation

Devour will be the challenge that tanks will be begging their DPS & and healers to run. It drops Soul Amalgamation, a tank-oriented item that gives a good amount of stats, a lot of armor, and a unique effect that blocks a set number of damage. As a must-have for all tanks unless they’re grinding for tomes or levels, you’ll definitely want to pick this one up.

Drops:. True Soul Amalgamation and Diamond Soul Nucley

Fountain will be the least frequented challenge of the bunch. It drops a mana-on-hit item that not even healers will find a use for. Some theorize it is the easier challenge and may prove to have value for going past that 10+ tier.

Drops: Eternal Spring Divine Ginko and Endless Power Fruit

Blackhole will be just as popular as tomb in 1.9 when the boss is fixed. It drops Particle, an item that gives a lot of damage and a unique effect that contributes a crit bonus & multiplier. For those classes that scale well with critical strikes and attack speed, this item will be a wonderful fortification.

Drops: Dark Matter and ???

Arguably the most popular challenge of the bunch, Return is the hardest to surmount. It drops a key that when in its final form, will give 50% attack speed, a fair bit of damage, a lot of armor, and allow one to open the Doom dimension. The doom dimension is where Raids begin, which is the beginning of end-game content. 

Drops: Doom Dimension Key and Doom Seven Key

You will notice a stepup in difficulty when you reach this challenge, the boss is unrelenting and his minions will push your group to the limit, pay attention to the time you are taking or the boss's dragonflame will seal your fate. Rewards an item that boosts physical damage.

Drops: White Dragon Scale and Pure White Dragon Scale