Ace Dungeons are solo content challenges. They offer 3 different challenges, each with 5 possible reward ranks (1 star to 5 stars). For each try, you can select up to total of 2 missions to complete. If you select only 1 mission, you only need to complete the selected mission to earn medal points. If you choose 2 missions in one run, you need to complete both missions in order to successfully earn medals. You will receive medals based on the rank earned per mission challenge.
Item Level: Any
Format: Solo dungeon
Location: Akasha’s Hideout (Fyrmount) and Golden Labyrinth (Hungry Caverns)
Entries: 4 daily

C Rank 30 medals |
B Rank 80 medals |
A Rank 100 medals |
S Rank 105 medals |
S+ Rank 110 medals |
|
BAM Sham Get hit X times or less by bosses |
200 or more hits | 80-199 hits | 30-79 hits | 10-29 hits | 0-9 hits |
Speed Racer Clearing in X minutes |
8:00+ | 7:00-7:59 | 5:00-6:59 | 3:00-4:59 | 0:00-2:59 |
Combo Lock Clear with X or higher combo hits. |
20+ combos | 50+ combos | 100+ combos | 150+ combos |
For example, if you select both the BAM Sham and Combo Lock challenges, and you complete the dungeon with 26 combos and get hit 0 times, you will get rank S+ in the BAM Sham challenge and rank B in the Combo Lock challenge. This will net you 110 medals for the BAM Sham challenge and 80 medals for the Combo Lock challenge, for a total of 190 medals for that run.
However, if you decide to have your challenges selected at random, you will receive a 10% bonus. Two random challenges will be activated if you go this route. You would have earned 209 instead of 190 medals in the example above.

Along with the medal rewards, you can earn various loots as a dungeon drop from the final boss.
http://en.tera.gameforge.com/news/page/challenge-dungeon
since yesterday I cant enter Lilith Keep in Ace Dungeon (yesterday it was possible). I dont know why I cant mark this dungeon to enter. I have a story quest with it and now I dont know what to do. Please help!
Anyone know why the combo count stops counting from time to time for some reason?
Do you mean between fights or during fights? Combo counter ends after a few seconds of not hitting something or when you get hit.
Curious. I ran GL on my reaper and was able to collect the VG. WHenderson I ran it on my mystic, no vanguard popped up.
It might be that your item level could be too low or that you ran out of VGs on your Mystic. Those are the only two plausible options I could see for the VG to not pop up.
Yeah, that was the issue. Have full DN gear on mystic but never enchanted it.
Will the etchings be tradeable? Are they convertible to tier 3?