Leveling is all about completing a series of quests. There is no longer experience points in the game. Levels unlock Ability Score points, Powers, Feats, and content, but they don't give you better stats, nor Damage, nor HP. Maximum level went from 80 to 20 with Mod 21, which changes nothing apart from the number. This is to put Neverwinter more in line with the Dungeons and Dragons pen and paper game from which it's derived.
Here are the requirements for each level :
Level 1 : create your character
Level 2 : complete Valindra's Siege quest (tutorial)
Level 3 : complete The Missing Doomguides (Neverdeath Graveyard)
Level 4 : complete The Emissary of the Dead (Neverdeath Graveyard)
Level 5 : complete The Clockwork Tomb (Neverdeath Graveyard)
Level 6 : complete Relic of the Past (Vellosk)
Level 7 : complete The Shadow Falls (Vellosk)
Level 8 : complete Into the Wolf Den (Vellosk)
Level 9 : complete Sealing the Crypts (Ebon Downs)
Level 10 : complete The Drowned King (Ebon Downs)
Level 11 : complete The Throne of Idriss (Ebon Downs)
Level 12 : complete The Goblin Warrens (Icespire Peak)
Level 13 : complete The Icehammer (Icespire Peak)
Level 14 : complete Icespire's Frozen Heart (Icespire Peak)
Level 15 : complete Quenching the Flames (The Chasm)
Level 16 : complete Cathedral of Madness (The Chasm)
Level 17 : complete Source of Corruption (The Chasm)
Level 18 : complete Xorlarrin Outpost (The Whispering Caverns)
Level 19 : complete Wrathforge (The Whispering Caverns)
Level 20 : complete Illithid Enclave (The Whispering Caverns)
Adventures
Adventures are your immediate goal once you start the game. They will reward you with many things, including Boon Points and rough Astral Diamonds. Undermountain is one of the most important of them as it will give you access to expeditions which can reward rough Astral Diamonds, Artifacts, good Companion Gear, and some Equipment.
Campaigns
Campaigns are long term goals which require repeating quests either daily or weekly, generally for about a month or two. They reward Boon Points, and often give you access to a specific dungeon and keys for their chests once completed.
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