Random Hodir is Random. And hodir is certainly not as easy as all the strat sites make out it is.
The two main issues are tank threat and DPS. Maximising your use of all the buffs, and making sure your tank can hold threat once you do get that right.
So here is the collection of information I have found trawling the intertubes. For some reason, there seems to not be a place where it is all collated - so I hope this comes up high in the search engines.
1 tank (no Frost resist gear required)
20ish of your awesomest DPS (which is probably your entire group!)
some kind of frost resist buff/aura/totem
Boss position: There are 2 schools of thought to this, hold hodir near the rare cache (so the adds gravitate to the middle, making them easier to bust out) or Tank hodir in the middle (and move him around a bit to keep melee with starlights as much as possible). We found that we are getting better DPS keeping hodir in the middle, but your mileage may vary. Both positions are valid.
Movement: This is a high movement fight. The reason for this is you cant get your stacking debuff go more than 2 stacks (or the healers cant keep up), you need to get into starlights and also be near toasty fires and get out of the way of falling snow. Tanks need to try and keep hodir as stable as possible, especially if tanking in the middle as it is VERY possible to move hodir accidentally into melee range and suddenly the mage sitting safely on 120% threat is oneshot (as melee range is 110% threat and you pull, as opposed to 130% for ranged)
Releasing Adds: Everyone releases adds as we engage Hodir. We mark up the mages and the shamans and release them first. The second time, we allocate a team of ranged and melee to get the adds out. Generally, these are the most bursty classes generally hunters and paladins. The last time, we only get out the mages and shamans to get back onto hodir asap.
Toasty fires and the Singed debuff: this stacks 25 times and then only requires 1 hit every 25s I think to keep it up. Explosive shot has 4 chances to replenish the stack for each shot, so probably should be included as much as possible in a rotation. Keeping this up is vital to killing hodir in 3 mins. For those people for whom movement is an issue (channelers or those with longish cast times as part of their main rotations) you need to get yourselves to a toasty fire as soon as you can.
Starlight: For those that value haste, this is probably a priority for you to get into.
Storm: There are reasons this should be in the ranged - the main one is that all the other buffs stack stupidly well together. Ranged are more free to move around than melee are and are able to get all 3 buffs at once (and should be actively seeking to do so). Singed also will benefit more from storm. The long and the short of it is, allocate your biggest ranged DPS (in this case, generally mages and warlocks) into a group of about 5 or 6 and mark them up. Everyone should be taking the storm buff to that group as soon as possible. Yes, it is possible for mages to crack 20k dps if all the planets align. I nearly fell over when I saw it with my own eyes!
Tank threat: This is a big problem due to the nature of the DPS requirement (to deliver 32.5 million damage in 180s by 20 people each person needs to AVERAGE just a smidge over 9k dps). Obviously, you need to have threat gear on. Pally's can benefit from the 25 stack, warriors have vigilance, DKs have their AM shield to help with frozen blows, and I have not yet read an account of a bear MTing hard mode. We use a Pally Tank and that seems to work the best.
But even then, threat is often an issue. 1 solution is getting the storm buff to the tank... but this gimps raid DPS. The best, but most delicate, solution is get a ranged to pull threat, taunt off them then get the ranged to aggro dump (ie hunters FD, mages invis, hand of salv, sould shatter etc etc). Doing this once or twice will make sure that firstly the ranged are not actually holding back (very important) and secondly the tank will build threat faster than they normally could. We use this to great effect.
When any of the ranged DPS in the marked group starts to get close, they call out that they are going to go for a threat pull. Our Pally tank then watches and waits for Hodir to change aggro and immediately taunts back, and gets the benefit of the extra aggro. This will take a bit of practise and some clear calls over your VoIP of choice. But it is the single most effective way of dealing with the threat issue we have found.
Cooldowns and heroism: This is best not blown at the start. You want the best possible moment to do all of this and it requires a few things to set up. You need the tank to be ready with good threat, and his taunt OFF CD (just in case). You want that singed stack to be at 25. You want frozen blows to be done, and you want a good number of fires, starlights and the storm buff to be in a good place. You want the full 40s of heroism to be used. This is best achieved AFTER the first flash freeze. Call heroism and save your CDs for this.
Flash freeze: Never get caught in it. Duh.
Frozen blows: There should really only be 2 frozen blows during this fight. A ret pally can use DS in conjunction with bubble if you have a low performing pally (ie a holy pally in offspec is a good example, like ME!). The other one should be covered off by a healer. Divine hymn should account for it exactly like in XT hard mode.
Healer makeup: you can pretty much take whatever you want, but Pallies should be last on your list due to their very static nature and lack of AoE heals. You want your best AoE healers and one kinda sorta MT healer. 4 at the most.
DPS makeup: Ranged heavy is preferred.
I think that is all the relevant information. Making it all happen smoothly is not as easy as people seem to be making out on the strategy sites! ARGH! I hate that!!
Making sense of the information
The way we managed to get this done was as follows:
Prot pally Tank (taunting when necessary)
Tank Hodir in the middle
6 top hitting ranged to stack up and stay on boss and be marked for all storm buffs
All other ranged spread out
1 group (hunters/ret pallies - but a team of 6 burtsy players not in the big hitter group) allocated to add extraction
Explosive shot to maintain singed.
Found that an ele shammy helped a stupid amount with DPS even if undergeared or an alt/offspec.
There will be a lot of sacrificing goats to the RNG gods, and for a long time you will find that your goats are not very pleasing. Don't lose heart! If you are close to the line one attempt might be 10% and the next might be a 40% simply based on where your fires, and beams and storms end up! Just keep practising getting that storm buff to the ranged group and getting adds out as fast as possible. Eventually, you will all get it right and hodir will die.
This is a very difficult strat to explain - if you have any ideas or require clarification please comment!