quartz dust
To teach players the basics and the details of the dungeons.
Ideally: Allow players to choose their hero, then fill the party with AI bots (no queue time, no griefing, nobody telling you how fast to go - yay), do a mini-version of each dungeon, representing each of the mobs you can meet there and the boss/es, plus add visual tooltips e.g. for interruptible/non-interruptible spells, cleansable/non-cleansable debuffs etc. If needed, tooltips can have a "Close" box and pause the dungeon while people read them, it doesn't matter.
Realistically: Update the Dungeon Codex with this info and make it more prominent during the Tutorial / first-time playing a dungeon (in all seasons, so it doesn't annoy returning players), please? 🙂