Jade Spirit

The devs told us exactly how MoP weapon enchants work at the link below.

http://us.battle.net/wow/en/forum/topic/6397900436?page=8#154

I'm pasting it here in case they retire the beta forums after release.

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• River's Song: 4 RPPM on melee attacks that land, or are dodged, or parried.
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• Dancing Steel: 2.3 RPPM on melee attacks that land.
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• Colossus: 6 RPPM on melee attacks that land, or are dodged, or parried, with a 3-second cooldown.
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• Elemental Force: 10 RPPM on damage or spell damage/healing
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• Jade Spirit: 2 RPPM on spell damage or healing, 50-second cooldown.
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• Windsong: 2 RPPM on damage, or spell damage/healing.
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Edit: As of 10/15/12, Windsong and Elemental Force now proc on all damage and healing, including melee, ranged, direct and DoT.

They now trigger on the new "Real Procs Per Minute" (RPPM) system, which is weapon speed and instant attack independent and fully detailed in this blue post.

http://us.battle.net/wow/en/forum/topic/6893549789

Edit 2: As of patch 5.1 Dancing Steel, Jade Spirit, River's Song, and Colossus are on the RPPM system also.

Edit 3: As of patch 5.2, Dancing Steel now has a 15% greater chance to activate.

Source: http://us.battle.net/wow/en/blog/8896363/52_The_Thunder_King_Patch_Notes-3_5_2013

Best weapon-enchant in MoP for casters ...

... but has it a decent glow?

[spell=104993]
SpellID - 104993