Has anyone something in this game that he or she didn’t obtain during certain time, and now it’s not obtainable anymore, or is obtainable but you can’t get it.
Il start , and for me is alliance Marshal armor or now replica. It requires rating in Arena or BG that I can’t reach.
More xp from timewalking
Incoming “MT appearances” and the obligatory “bring back the MT Blizzard!!” replies.
I managed top get some on EU account, but I don’t have any on US account or my main account now
The MoP challenge mode gear. In particular I really would have liked having the paladin and monk sets.
It’s totally my own fault. I was kind of intimidated by challenge modes, I didn’t know how tough the golds were or how salty teammates would be if I messed up. So I put it off and put it off. Didn’t attempt a single one by the time MoP ended. 
The Gul’dan staff and cosmetics but the one that really gets me bummed…
MT appearances…
And please bring back the MT blizzurd
^
I came here to say this
For me, the biggest one is the Swift Zulian Tiger. Its been one of my favorite mounts since I started playing but I got lazy and never farmed properly before they ruined replaced ZG. I know it’s one the BMAH but I’ve only seen it once and it went well past my pockets pretty quickly.
The only reason I want 10M gold is to buy this mount. I will do it without hesitation if I ever, you know, get 10M gold.
You absolutely can! You just have to sign up for rbg groups in the group finder and keep playing and you’ll get it. Theres a lot more to contributing to a team win than just healing, so with experience youll learn habits thatll help you be where you need to be at the right time.
If you unlock it on horde itll convert to alliance if you play an alliance priest
Don’t give up on it, its lucky its still in the game and obtainable 
For me it’s the Corrupted ashbringer. I know they have an artifact appearance for ret pallies but it isn’t the same imo.
Black Harvest for my lock. Got the green fire, but wasn’t playing when the title was available. So jealous when I see another lock with title, hats off to you
Boring one here. Tier 3. I do wish we’d pushed harder when the raid was available, but everyone in guild was all about TBC incoming and could not be bothered with Naxx.
I have tier 0, 0.5, and 3 on my classic wow hunter. I also have corrupted ashbringer. too bad i will never be able to get them on retail because im broke.
i also have a pair of hakkari twin blades sword i miss them when i play retail.
My sanity. 
But in all seriousness… I wanted Anathema/Benediction and the Druid challenge set from Mists.
Tyrannical paladin elite set
That stupid primal flamesaber mount. I didn’t want to have to learn whatever game the promotion was attached to. It’s ugly and I’d never use it, but it’s now a permanent -1 for me.
Mimiron’s Head. The blasted thing evades me no matter how many times I try.
Then tonight, I see it on the BMAH for 1.1m gold, and I’m short about 300k. q_q
I still regret not getting the MoP legendary cloak on ALL of my characters. Why? Because.