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Physick spam for the tank, Rouse/WD for defensive (should heal ~2000) and physick/lustrate for landmines and brainjack/homing missile bait. If you do this you should be at max MP for the entire fight. You should use piety build for t8, crit sucks here since you don't need adloquium. If you go piety build (~5000MP) you will regen 125 MP per gcd with good aetherflow use (physick = 133MP).
Don't need aldoquium for dreads if tank is using convalescence or brainjack target. No need to use succor for early phases: if dps are not topped off with WD then sacred soil (10%)/fey covenant(7%) (if Eos). If you have the time use proshell protect outside fight and enter as SCH (15% MDef boost = 5%). If you use all 3 that's ~20% magic damage reduction. You can use succor during three tower phase for defensive only.
If you are really good you can ensure embrace is used all the time so you don't have to stop physick spam (or let embrace heal tank and you physick other target)
TLDR: adloquium and succor are waste of MP, if you don't use them you won't need mage ballad. Only use them if you are behind in gcd/panic.
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So, I ended up solo healing a large part of this fight as our whm disconnected after 5% in and came back at 10% left on boss. Never needed Mages Ballad but rarely needed Lustrate either, so I just used Energy Drain every now and then and still used a succor to be on the safe side. I had around 4.3k mp back then, think I had around half my mana left when the fight ended. Didn't plan on it, but worked out well.