Rogue Bundle
Dreadlord's Nightstalker:
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Equip: Unlocks the ability to /taunt: Rogue bends over and releases flying daggers
Equip: Having slain your foe the Rogue automatically performs a Fatality
Equip: Permits you to harvest the Vanilla herb now visable in Azeroth with any character with the Herbalism skill on one WoW account: (used to craft ''Vanilla" weapons/armor):
Once crafted: can duel weild FAN dagger/swords
While wearing the Nightstalker's armor the Rogue may permenantly stay stealthed so long as the Rogue remains in a Zone or City in which Night time is present and/or the Zone is darkened i.e. Duskwood. The Rogue gains increased movement speed at night and all bonuses wear off when the armor is removed and/or broken until repaired otherwise
Druid could get a Treant or Furbolg feral set or even a Dryad balance set; a bonus could include now being able to communicate with animal NPC/Mobs and receiving special quests (Efsee the cat in Lakeshire Redridge finally says something you can understand and starts up a new quest chain)
TL;DR: Transmog Gear with bonuses that unlock abilities but DON'T specifically add bonuses to the character itself (Str, Spirit, Stam, Agility etc.)