I don’t want them to place such rewards behind difficulty wall until they really work on PVE balance. It’s not like I’ll be able to choose which character to play if I want Miko’s skin…
Miko is pretty good PVE, though! My main is arguably one of the worst PVE characters, so I did factor this into my suggestion 
His damage is, well, not impressive.
What is hard for Mellka, will be easy for Oscar Mike, Marquis, Orendi, etc. Current PVE balance is in too bad state to introduce hard challenges you have to beat with every hero.
Right, but it’s equally hard for all Mellkas. 
I don’t really understand why it’s important for every character to be equally effective in PVE, given it’s non-competitive, but then I don’t have that completionist urge to unlock things for characters I don’t like to play. Which seems to make me an odd one out often.
Miko crits well with their kunai, and the damage mushroom is effective, so I feel they’re in a decent place for a PVE character. El Dragon, on the other hand, is going to have such a grim time of it…
Because if they are not, the whole point of hard challenges vanishes. If they are hard for weakest heroes, they are not hard at all for strongest. If they are hard for strongest, they are impossible for weak heroes.
I see your point. I’m kinda down for some impossible challenges, though. Also, if there isn’t any meaningful content behind a “difficulty wall” as you put it, does that mean that this game’s PVE is fundamentally broken? Because even playing story as Miko or Mellka right now is too simple to be fun 
I don’t know. There is no reward for difficult content right now (other than being proud of getting all gold) and I’m happy with it. I like difficult content only when I can choose to play it based on my mood, not be forced to play it.
I’m curious why you say “forced.” Most of the cast can’t plausibly get a Penta, but that doesn’t mean we’re all being forced to play El Dragon and Orendi, right?
Edit: because we otherwise can’t unlock that title, i mean
This is a pretty sketchy analogy now that I think about it… I guess I’m trying to suggest that having an optional challenge and reward exist out there could be a nice thing, an incentive, even if some characters in principle are more likely to get it. Somebody will get that Reyna penta eventually, surely, haha.
Also, just to be clear 
By forced I mean I have to do it in order to get something valuable for me. Like skins. I like it when challenging content has no incentive to beat it other than your personal desire to spice up your life, test your skills, etc.
I mean, when there is a reward, not just congratulations text and an achievement mark, it may become a work: you don’t like the process, but want a reward. But when you like the process, it is already a incentive to play that content and you don’t need more motives.
As I understand it, you want to wear the skin while you play the game; I want to play the game so that I get to wear a skin, haha
I do understand you, I think, even if we’re different.
I also play for the game first and foremost. I’ve played around 120 hours on Mell - there’s no unlocks or rewards for that, just the opposite! But I’d just love to have an alternative to the old Master skin and titles as a way of showing our commitment to mastering the intricacies of the game. 
I kinda doubt they, let’s say, have enough resources to do this. Current scoring system is completely broken, PVE balance between characters is ignored, difficulty scaling has obvious flaws and there is no word on fixing it. There are no reliable instruments/scales in the game to measure your skill or “mastery”.
I’m just not sure whether the intention is for the unlocks to be challenging, or whether it’s kinda automatic - you do the mission x times, enough to push to its final stage, and you’ll be guaranteed both skins. An incentive to buy the DLC, basically.
Seems like they want getting 100 OPs to be challenging, at least:
Give me any team of 5 and any advanced stage.
I’ll make it happen.
All characters are not created equal true but this game has yet to present us with anything close to an insurmountable challenge.
No one character should be able to hit the 100 mark playing solo and I hope that’s the case come this Thursday. Some characters truly have an inherent advantage for PvE just based off their design but no character is entirely unviable and useless with the right gear and more importantly the right team comp.
Why?
More like “you can play weak character if other players pick strong ones”. There is no magic comp to turn any weak hero into a strong one, because heroes are balanced for PVP, but PVE is a whole different case. What is good in PVP is not necessarily good in PVE - not because you don’t have right teammates, but because it is just not good. PVP favours burst damage, right timing, sudden attacks, CC - these all help kill other players. PVE requires solid continuous DPS backed with reliable survivabilty for a long time, not just in a short fight against a few enemies. If you don’t have them, you are a dead weight to your team.
For arguments sake give me a bad PvE character
one that comes to mind off the top of my head, pendles is atrocious for pve
For example, Mellka and Deande were always underperforming in PVE. Not plain bad, but significantly weaker than many others. El Dragon will most likely suffer in PVE after the patch, being even more glassier and without his cannon.
I’d measure PVE strength of a character by how many weak players you can carry through a mission with him. Mellka and Deande are very far from top in such list.
Solo maybe
In 5 mans you have infinite revives, amazing aggro pulling, high sustained dps with back attacks and back attack injection crit spamming during miasma with Firmware and VoZF is amazing top tier dps right there.