For spine only gear I change out is my Scintillating Rodswand for Hungermouth and 2 trinkets, I use Bottled Wishes and the Necromantic Focus (throw a swp on 2 bloods just b4 the plate lifts to keep your Soul Fragment stacks) then reforge the gear more at towards mastery>crit>haste.
I use a site to do my reforging for me as it saves me a tonn of G and if you have the Reforgerade addon you can just copy the summary into the addon and it will reforge the gear for you.
This is a Template of the Stat weights I use for spine WoW Reforge
If you plug yourself into that that's how I reforge for the fight.
For the fight itself all I do is have swp on the Amalg and flay it like nuts till the fiend cooldown resets, if you have a arcane mage you should steal his FM, we have x2 Spriest and x2 mages on that so we both get FM.
I'm also on Corruption breaking duty and still manage to reset it 98% of the time, the other 2% is really unlucky with crits or I get gripped every cd.
Most of the time doing this I am top 3 for tendon dmg (At least 1.3mil per first lifts and about 1mil for the 2nd lifts) this week was top as I got a few huge MB crits and my staff duped them, don't claim to be amazing but I pull my weight (when Australian Internet lets me that is lol )
edit: Also these are my 3 main macros for the fight, what I do is spam this first one as the plate is lifting and get x2 crit debuff on the the tendon then pop the wings/trinket/fiend one then mb, spike etc etc
Code:
/tar boss2
/stopmacro [noexists]
/cancelaura mind melt
/cast mind spike
/cast [target=boss2] mind spike
/tar boss2
Code:
#showtooltip Archangel
/tar boss2
/stopmacro [noexists]
/cast Shadowfiend
/cast Archangel
/use 14
/tar boss2
Code:
/cancelaura mind melt
/cast mind blast