You are only able to go into Hard Mode in presearing upon reaching level 20.
Death Penalty does occur upon death.
Regular tomes do not drop, only Capture Tomes which allow you to learn Signet of Capture.
Gwen will be buffed to heal for slightly more health.
Hidden Stashes are replaced with Locked Chests, however the merchant will not start selling lockpicks, they will only drop rarely from hard mode monsters.
Hard Mode monsters will drop the same items as their Normal Mode counterparts, with the exception of Lockpicks and Capture Tomes.
What this introduces:
Weapons only through locked chests, which can only be opened with lockpicks rarely dropped by charr killed in hard mode across the wall.
The following skills are now attainable to presearing characters through the use of Skill Capture: Barrage, Favorable Winds, Banish, Heal Area, Infuse Health, Faintheartedness, Mark of Pain, Energy Burn, Illusion of Haste, Mantra of Flame, Conjure Flame, and Lava Font.