Ace Dungeons are solo dungeons you can do for minimal rewards. (And complete Vanguard Requests for Weekly Bonus.)
Dungeons give Vanguard mission reward for credit, some gold and XP, possibly Battle Pass tokens, have some drops and earn Ace Medals. To enter dungeons find Ace Dungeon Instructor in any major city: Hallik in Allemantheia, Vemmen in Kaiator, Armin in Velika, or Ramull in Highwatch.
Lilith's Trial was added in patch 80. It was initially full Lilith's Keep dungeon, which is ill suited for a solo run. Dungeon got later movement speed buff to skip the long corridors. It was later cut to include only last boss, which makes dungeon few seconds run for a geared character.
Patch 103 the new Ace Dungeon Lumikan's Trial is released.
Dungeons have 3 possible challenges, each with 5 possible reward ranks from 1 star to 5 stars. You can pick two or random challenge to go into a Ace Dungeon. Completing challenge gives more Ace Medals.
Requirements for best S+ class are:
- BAM Sham: get hit less than 9 times by bosses
- Speed Racer: clear under 2:59
- Combo Lock: do 150+ "combos"
"Combos" is badly defined. It simply means hitting bosses X times in a row.
As of patch v102 enchanting materials are removed and Ace Shop only has rubies for 400 tokens and some glyphs you already got from quests.