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Run it on Normal difficulty over and over, slay every single mob you can find, and they will give you reputation as long as you keep the tabard equipped. The best dungeon for farming reputation is The Mechanaar in Netherstorm. You can get the Silvermoon City Tabard from Magistrix Nizara in Eversong Woods, and then run dungeons in order to gain reputation with Silvermoon City. You can gain a lot of reputation by questing in Eversong Woods, but that might not be enough for Exalted.
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Note that the Heritage of the Sin'dorei transmog set is hidden and does not show up in the Appearances Tab until learned. To unlock the Heritage of the Sin'dorei you will have to level up a Blood Elf character to 120, reach Exalted with Silvermoon City and then complete a short questline starting with The Pride of the Sin'dorei. The Heritage of the Sin'dorei is the heritage armor set for Blood Elves. You can change the previewed race by clicking on the arrow below the picture on the armor's page.Heritage of the Sin’dorei – Blood Elves Heritage Armor Guide *according to the comments, you get all three colors of the Mag'har Orc's armor
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Once earned, you can use this transmog on every alt of that race. The ones of allied races require to level up one character of that race without a level boost (heirlooms are allowed) and gain the achievement (like Legado de los forjados por la Luz).
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