Merge glitching is when you disconnect/close the game right after buying an item from a merge shop. This will get you the item, but the server didn't had the time to remove the resources.
There are several ways to do it.
Easiest is with the tool gaffox made: https://www.mpgh.net/forum/showthread.php?t=1359548
Start with a low delay, and increase bit by bit until it works.
If you get the item but lose the resources. Lower the delay.
If you never get the item (but don't lose resources either). Then increase the delay. If this happens only once in a while, then I recommend to not change it.
The quests can't be glitched (cause you need to accept the reward)
So do the quest "Create the Doom Blade's Aura" AFTER you both got "Necrotic Sword's Blade" and "Necrotic Sword's Hilt"
Also "Time Lord's Necronomicon" doesn't stack, and "Bones from the Void Realm" stacks to 50.