For people with Dragon Amulets only. Do the hydra's lair quests and keep on doing it until you get the Wavecrest sword. There are multiple versions. Get the one your level is closest to. then, if it's higher than your current level, farm some (I recomend Dr Voltabolt's challenge.) And make sure to use an Energy or Fire weapon when doing the hydra lair quest.
By paying an unreasonable amount to get the necrotic blade of doom
the next best option would be to buy dragon coins and shop at Cysero's weapon shop
If you don want t pay for DC's but don't mind paying for a DA you can buy the DA weapons from the player suggestion shop by going into the inn at falconreach and selecting the "talk" option for serenity. there are also weapons in that shop that can be purchased using gold if you dont want to pay for anything
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when you kill hydra while coming to flaconreach you get the sword
The sword is called Aqueric Force. Do the "Its a Wash" quest from Valencia.
The Icy Sword can be brought from Dragesvard's Weapon shop or Moonridge's shop.
go to atririx in neropolice and random quest
if you are a gardian in adventure quest, you need to verified the guardian in dragonfable, so you can equip the guardian armor, you can get the guardian sword in willowshire, then go to the tower and get all the keys (the gems) then you will see a ghost guardian and press "shop", and there, you get the guardian sword.
you need to wait till frostval and then you got to get enough coals and the togsmas sword gift
there are a lot of good weapons, check out this link:http://dfwiki.com/index.php/Best_of_the_Best
depending on your level best damage is 50-80
there is 1 called brother's blood, and if you can find xan in falconreach, you do his powerful challenge.
The overall boss is unknown, however Shadowscythe (Necrotic Sword of Doom), is probably closest to an overall boss.
yes,it level up with you not like 51 it would be 50