Before reading this you can read about NPC at https://duelevolution.wordpress.com/2007/09/07/npc-duels/, http://www.yugioh-online.net/top/english/cpu/index.html
There are 2 Type of NPC First Type are Characters NPC from YU-GI-OH and YU-GI-OH Duel Monster GX. All of Characters NPC will stay at the same spot they don’t move between area and don’t remove from the game.
Second Type of NPC is Standard NPC (Non Characters NPC), They will change a spot almost everyweek and some of them got remove from the game and return to the game also.
NPC using old Ban/Restrict List and never change Deck Recipe follow New Ban/Restrict.
NPC will award you some Cloth/Uniform/Cards/Deck Recipe (Only Deck Recipe not a Cards with it)
For a List of NPC Awarding Item can see it at
NPC Duel Academy
(not finish yet I will finish it later)
You can see all of NPC and Item they given at
1.http://yowiki.yugioh-portal.net/?CPU (JP CPU Wiki)
2.http://www.ygo-academy.com/mybbprod/showthread.php?tid=854 (Yugioh Academy Board)