I was not sure if I should put this in strategy forum or here but anyways here it goes.
Last night I was tanking Mimiron (we just got to him few weeks ago) and I was dying a lot on plasma blast in phase 1, after which I figured I could not survive a plasma blast without a CD so I started poping cd's for the 1st 2 than Guardian Spirit for 3rd and in case we get to 4th I would die(which happened on all attempts).
So can someone check my gear and see if I have enough to survive it, lot of my gear is naxx 25 which I thought should be pretty decent for 10 man ulduar.
Also what other things can we as a group do to help me not die. I am usually not the tank but since summer attendance is been low and our regular DK and druid tank was not there last night I ended up tanking it and felt pretty sad after a total fail.
Your gear looks fine. And you're right, you do need a cooldown for each blast. We ran with a setup similar to yours, and P1 becomes a lot easier when your dps manages to get it done before the 4th plasma blast (that should be your goal). In the mean time, keep your healthstone, health pot and enraged regen handy for the 4th plasma blast, and make sure all your healers are expecting the huge burst on you, (PW:S, Earth SHield, it all helps) it's still possible to survive it, it's just not that easy.
you should be getting phase 1 of Mim down before the 4th plasma blast. BUT...I believe he does a Plasma Blast every 40-45 seconds (someone correct me if I'm wrong). If you're popping your Shield Wall for the first Plasma Blast, Last Stand for the 2nd, Healer CD for the 3rd...your shield wall should be back up for the 4th plasma blast, correct? Assuming you're glyphed/spec'd for a 2 minute shield wall.
You should have sufficient HP to live through a plasma blast with a cooldown. The only thing I could think of that would help is the 4 piece Tier 8 bonus, which you would have to cast Shield Block along side Last Stand - since 20% less magical damage by itself, I don't think, will get you through a Plasma Blast. Other than that, your stats/gear look fine to do Ulduar 10.
If you've got only 1 tank then you really should have enough DPS to get him down before the 4th blast. If you're not making that goal you're probably not going to kill him even if you have the cooldowns for it.
If you're using a second tank (and depending on your raid comp, having 2 tanks can be really nice in p3) then just have him taunt and take his CDs.
If you're popping your Shield Wall for the first Plasma Blast, Last Stand for the 2nd, Healer CD for the 3rd...your shield wall should be back up for the 4th plasma blast, correct? Assuming you're glyphed/spec'd for a 2 minute shield wall.
I am speced and glyphed into 2 min cd's and I could almost swear I had 5 secs left on SW when he did the 4th one(again there was so much going on that I might have just missed it) but I will keep that in mind again.
There are other tank saving CDs available depending on your raid comp.
Disc priest-Pain suppresion
Holy Priest-Guardian Spirit
Paladin-Hand of Sacrifice/Bubble
But ideally, as was stated, you should have him down prior to the 4th Plasma Blast. Even with 2 tanks in the raid we manage to down him prior to the 4th, and thats with some questionable DPSers. 2 Tanks Will make the encounter much easier. We found that taunting after each Shock blast(the AoE, i think thats what its called) worked best, made for much easier repositioning.