Merger Weapons commonly have requirements on items needed to merge for them or upgrade them, it all depends on the weapon.
with weapons
It's very easy. You just do a war quest in Falconreach, most times the reward is a stone of falcon reach tower. Good luck getting the Glory Weapons!
the doom weapons are level 8 weapons and do lots of damage.
U merge it w/ To Valencia and Never Ending Storybook
the three doom weapons i would say
do the packing up quest (part of the fire war chain)
you first need to reach chapter 6 in the frostvale story book and get into a place called breaking in. from there obtain coal merge coal with the items to form ur togsmas items.
In quests like defend the keep, sir jing's weapons and other ones
there are a lot of good weapons, check out this link:http://dfwiki.com/index.php/Best_of_the_Best
you can check it at Dragon Fable Wiki>Weapons>Weapons listings by level>Category:Level 16 Daggers
u download them at wpe pro or crash override
There is zangetsu (in both shikai and bankai forms) and you can get them from cicero's shop on dragon coins :|