Hard
Dungeon Scaling is in effect, but has less of an impact than Normal.
Favor is 2 × Normal.
Main XP is roughly 1.05 to 1.08 × Normal.
There may be more and/or larger encounters than Normal.
Enemies are always a higher CR, and have far higher statistics designed to challenge more prepared parties.
Enemy spell casters often have more and higher level spells.
Monster Damage Reduction, at their best, block only 75% of your damage instead of their true value.
For example: If your attack deals 16 damage, but the monster has DR 15/-, your attack still deals 4 damage. You can see it better against the DR 100 monsters: ghostly skeletons in Delera's and gargoyles in Stone Form.
Enemies can upgrade to a Tier 1 Monster Champion.
The quest's level is increased by 1 solely for purposes of generating better chest loot and comparing against the party's level for XP adjustment. Rewards from the quest's giver are unaffected.
Traps are greatly increased in difficulty, in terms of damage dealt, save DC and skill DC needed to disable them. They are intended to challenge decently-geared rogues of appropriate level.
Hidden doors and Lock DCs sometimes scale up a few points.
Enemy misses become Grazing Hits on raw die rolls of 15-19.
Rest Shrines can only be used once. Some quests have fewer shrines when compared to Normal.
Hard is intended for full, well-balanced groups of 6 players, or 12 if it's a raid.
Free to play and premium players cannot open a quest on hard unless they have already completed it on Normal or higher difficulty, or they underwent True Reincarnation at least once. They can use Hard Difficulty Quest Unlock Token from the DDO Store to bypass this limitation.