Buff Mist Dragon plz

[RopeDrink]

Meh, it really isn't all that difficult - it just happens to be in that sweet-spot where it is a) relatively new and b) not everything is telegraphed by humongous amounts of orange squares or circles.

1- Rime Wreath: boss begins with this, then uses one as an 'in-between' mechanic from then on (up until post-dive phase where it'll use three of them back to back). It's basically just an arena-wide AoE for moderate damage.
2- Blue Marker: ie. Freezing Puddle Breath. Try to aim it so that the resulting blast leaves as few ice-puddles as possible. Getting an entire team dotted with freezing would be extremely painful, and leaves less space in the arena to move safely if it is aimed right across the arena center.
3- Star-Shaped * AoE (Single). Self explanatory, complimented by big orange markers.
4- Fog Phase 1 - Kill dragon heads. Self explanatory.
5- Repeat 1 & 2.
6- Double Star-Shaped AoE. It helps if people are grouped for this part, as having them stacked on eachother (anywhere) is infinitely easier to dodge than having them spawn in two random places and overlap across the arena.
7- Dive Phase - spread out and have everyone run around the arena in the same direction. Someone will eventually spot the dragon in the mist. When players stop running, that is an obvious sign they've found the 'line'. Repeat twice.
8- Triple Rime Wreath followed by Blue Marker into Star AoE into a general mechanic reset back to No.1

Here is the above boss rotation in video form, sprinkled with a dose of "DC DPS" to prolong the fight.

https://www.youtube.com/watch?v=3ySbYwjH32k

Things that help:
Healers capable of pre-casting Esuna (Ice DoT).
Healers capable of pre-casting AoE heals vs Rime Wreath.
Ranged Damage of any description vs anyone encased in ice. Even a WHM Aero I (2k impact damage) is sufficient.
Players who aim the blue-markers appropriately.
Players who know when to stack for the AoE marker, though this isn't mandatory - it simply helps. Nobody likes becoming an icicle.

[Rongway]

7- Dive Phase - spread out and have everyone run around the arena in the same direction. Someone will eventually spot the dragon in the mist. When players stop running, that is an obvious sign they've found the 'line'. Repeat twice.

It takes much less effort than that.

You really only have to run to opposite sides of the arena. If neither pair sees the dragon, then the dragon is clearly not diving through party. It's not necessary to search the entire perimeter.