I've collected from various threads on different forums about Blue Mage being a viable tank, including the post here on BG about tanking Tiamat as a BLU/WAR using Magic Defense enhancing spells, etc.
Here are some questions I had, that maybe I could gather some of your expertise to answer:
1. How does a BLU/WAR's defense measure up to say, a PLD/WAR?
I tried using BLU/WAR in basic sky farming today to see its feasibility of tanking versus Zipanca and Faust. I was able to get my DEF up to 703 with Defender and Tav. Taco, along with Protect IV. I'm also probably ignoring the enormous +VIT equipment a typical PLD would have. Holding hate was an issue, but I'm sure once AF is released and my spells aren't resisted all the time, it'll help a lot. I was going for the "stun" tanking approach, using Provoke, and basically just blowing my MP on stun after stun move while MP was kept readily full with a BRD and RDM in my PT. I suppose the DEF of 703 could also be boosted up, if I had Crimson/Blood gear and a Genbu's Shield to help DMG reduction. I was taking an average of 118 DMG per normal hit from Zipanca, and held hate only by means of Magic Fruit and Healing Breeze, but those are quite costly MP-wise. Brings me to a second question:
2. What would be the optimal gear set for a Blue Mage tank?
There's a lot I don't have, and won't have for awhile; hence I can't test immediately, but I'm interested to see the effectiveness if any. This includes Nashira, Homam, Crimson gear. What others am I leaving out?
3. What kind of spell set would you use?
Does the constant stun type spell set seem feasible, or would you go with a different type of spell set? Plasma Charge vs. Reactor Cool? I have 4 merits into Blue Magic skill right now, and I wasn't able to land more than half my Head Butts, or any of my Actinic Burst (Flash), Tail Slap (stun), Temporal Shift (stun), or Frypan (stun). I'm sure this will change with AF.
4. Has anyone tested the effectiveness of Magic Defense Bonus enhancements?