Thanks to Locked of SouthPerry, the community of Basil Market, and Max from Orangemushroom, and KamiNoBeniMizu (that's ME!) for the sprites, names, and stats of the items.
Sets are... well, sets. If you equip many equipments that are part of a set, you'll get some neat stat boosts! Here, I'll list them by level. I'll even show you how they look (in the case of the Tempestuous set, if I can log into MapleStory and take some screenshots that is... -_- *SIGH*)!
Weapon/Armor
Dragon Set (Level 110)
Eclectic-Briser Set (Level 120)
Necromancer Set (Level 120) [Hilla]
Muspell-Jaihin Set (Level 130)
Royal Von Leon Set (Level 130) [Murt's Shop]
Pensalir-Utgard Set (Level 140)
Empress Set (Level 140) [Cygnus]
Japanese Set (Level 150) [Mori Ranmaru]
Tyrant Set (Level 150) [Magnus]
Root Abyss Set (Level 150) [Root Abyss]
Sweet Water Set (Level 160) [Commerci]
Absolabs Set (Level 160) [Orchid]
NOTE:Orchid is currently ONLY IN KMS.
Accessories
Boss Accessories (Level 100-140)
Gollux Set (Level 120-150)
Event Sets
Mesoranger (Level 75)
8th Anniversary (Level 79)
Legend Maple (Level 80)
Grand 8th Anniversary (Level 99)
Tempest (Level 100)
Tempestuous (Level 130)
