I'd like to hear your thoughts on Zomborg. While I may not agree with your self-proclaimed expertise, I know you main (or at least used to) Sleepers and Exiles, so I'm interested to hear you out.
As for Yagron, if you're getting nothing out of his first activation you're doing it wrong. This is the Exiles, remember? The faction that wants to discard cards? Yagron allows you to do so consistently and you even get to choose which card you're discarding, which is great. So turn 2 you can discard an Unstable Demon (or, if you'd like, a Spontaneous Combustion), then next turn you can pay 1 for it and activate Yagron again, getting an 8/8 demon. Calling them 4-costs is something of a misnomer, since the second 2 goes towards making the next one and they have an exile cost of zero--meaning that if you discard them to something else, like Demonic Presence, you can recast them for free. Moreover, Yagron is a card advantage machine. He's perfectly fine, certainly more playable than Hinekri or AC Hellbringer. Yagron's targeted discard allows you to set up Descension casts, Combustions, and any other exile cost you want while still netting you sweet sweet card advantage. He's good. At the very least, I don't think he needs changed.
You claim to disagree with me but agree with most of what I said
First off you are right that I ONLY
play Sleepers and Exiles, sometimes I will mix in FD. Furthermore keep in mind that I ONLY
play 1 Purity decks (As in 3 Purity Sleeper or 3 Purity Exiles, etc..) I know that balance and mechanic feasibility expand a bit when you throw a different faction into the mix. But I dont do that, so I can only talk about what I experience.Before I start I just want to say that I use the term "Drop often. If anyone doesnt know what that means it just means cost. A 3 Drop is a card that cost 3 resources. Meaning that you can drop the card down, when you have 3 resources. Ergo, 3 Drop.Zomborg
Being that I run 3 Purity Sleepers it is a given that I must run 3 Inevitable Deads, they are just TOO valuable. They allow you to go from a 40 card deck to a 37 card deck which helps with consistency, they also allow to you discard on turn 2-3 if you play your first few cards from your command zone allowing you to discard a Risen of Avarach or Sleeper of Avarach and do some cool combo's.
Furthermore Sleepers have almost nothing but 2 drops. Risen of Avarrach, Sleeper of Avarrach, Inevitable Dead, Plaguebearer, The Last Sleeper: ALL OF WHICH
are essentially a MUST HAVE
in your sleeper deck. And that doesnt even include their 2 drop spells.
It is just a weird experience where you have no  drops, then Turn 2 comes around and you have to chose between 7  drops; And to be honest, in my experience, playing Zomborg on Turn 2 will hurt you more often than it will help you. Because, first off, he has the stats of a  Drop, also you cant really attack or defend with him or else you risk losing him and even then a Fire bolt or Lightning Blast can still make that happen. So for the most part, if your opponent has ANY early characters you wont risk putting Zomborg on the battlefield, so he sits in your support zone. So you have now wasted both Turns 1 and 2. Turn 3 you waste another resource because once again all you have are 2 drops (Sleepers literally only have 1 viable  drop which is Parasite, which is reactionary so you wouldnt play it on Turn 3 90% of the times). Because of all of this by Turn 4 you have already essentially wasted 4 resources and have no real early game pressure... And the sleepers are not known for their late game.I went on a bit of a rant there but my main point is this.
1) You want to play Zomborg early because if you play him late chances are he will either die or you will die because he transforms.
2) There is no real good time to play him early game because he slows down your pace, leaves you defenseless, and almost ANY other sleeper  Drop will serve you better. (Bloodthirster, Inevitable Dead, Risen, etc...) They all have super strong effects that allow you to take control of the early game.
So you cannot play him early, and you cannot play him late, so when do you play him? I personally just got to the point where most of the games I played him in I regretted it so I just dont play him anymore. I own multiple copies of him including a Gold copy and do not run him in any of my decks. Now perhaps if you go 2 Sleeper and 1 other faction there is some combo someone can do that would make him more feasible, but in my opinion, in a 3 Purity Sleeper Deck, Zomborg is unplayable... At least not at a competitive Level.
Changing him to a  Drop would solve this problem because you were not playing anything on Turn 1 anyways. He almost just becomes an Ixxi that could pay off later but atleast then you treat him as you should. You can go on the offensive with him because after all you didnt really invest anything in him, and you can sit him in your support zone if you want to.
Furthermore him being Unique prevents spamming, he would still be 4/4 at Turn 2 so the opponent still has access to the same options of dealing with him. He would evolve on the same turn. And doing 2 Damage to your opponent on Turn 1 isnt game breaking. The only change is that he is not longer made nonviable due to way better alternatives.
This is actually something I just thought of but at the same time, I would also entertain him being changed to a 3 Drop with 4 Evolutions. With his base stats being changed to 8/8. Or Make him evolve with every character that dies while he is in play. The way he currently is is just unplayable IMO. But that is just one Sleeper players opinion.
^ Wow that was long, sorry for the wall of text. Now time for Yagron. Yagron
The combo with Yagron you just mentioned is his only saving grace. But even that Combo is lack luster at best. The issue with Yagron is this: You pay 2 to discard a card!! this is AWESOME because you get to use the Exile mechanic!!! The problem is Exiling a card doesn't really give you that much of a benefit. For instance Unstable Demon is 10/5 for 3, which is fair stats for a  drop. If you Exile him you get him for 1 cost, WOW!! But you paid 2 resources to discard him... So what did you really save??? And remember, the Unstable Demon/Yagron Combo is the BEST you are going to get. Do the same math with other Exile Cards:
Unstable Demon = 1 Exile Cost + 2 Discard Cost = 3 Real Cost
Spontaneous Combustion = 3 Exile Cost + 2 Discard Cost = 5 Real Cost.
Demonic Disciple = 1 Exile Cost + 2 Discard Cost = 3 Real Cost
Cresil, the Mad = 5 Exile Cost + 2 Discard Cost = 7 Real Cost
The same thing goes for every other Exile Card. But I know what you are thinking.. Wolf... My poor confused friend... you have forgotten that you are getting a  cost 8/8 Demon! Well not so fast. We have to consider 3 things.
1) You cannot play this Demon
2) Just how good is an 8/8 Character?
3) Exile Resource Curve means that 2 Drops are bad!
4) Cards sitting in your hand is bad
5) Pay Attention to Resource Curve LightmareYou cannot play this Character?
I am certain no one is arguing that simply getting a 8/8  Drop is a good thing, Yagron is good because it gives you an 8/8 that you can get for 0 Cost... Or does it? Because once again to discard it you must pay  Cost. So EITHER WAY
you are going to end up paying 2 Resources for this 8/8 Demon. Unless you use a Cresil or perhaps a Madness but at that point you might as well just put ritual master in your command zone and save yourself the trouble...
So the caviat is that while it may seem like you are getting a 8/8 for 0 Cost, you are really getting an 8/8 for 2. Which is decent right? Wrong, keep reading.Just how good is an 8/8 Character?
I mean an 8/8 Character that you cannot possibly use until Turn 4. Remember you discard a card on Turn 2, and the 8/8 Demon appears in your hand on Turn 3. Since it makes no sense to play it,
(because if you can play it then why not just discard it and get another 8/8 Demon.) So you discard it on Turn 3 and it appears exhaust in your support zone on Turn 4. You can then use it on Turn 5. THAT IS 3 TURNS!
I am not saying it is HORRIBLE. Because an 8/8 for 2 cost is pretty good, i guess. But an 8/8 on Turn 5 that costs you your 2nd Turn AND your 3rd Turn seems ludicrous. I want to expand on this a bit more but this is running long enough so I will leave it on that. The card is very clunky.Exile Resource Curve means that 2 Drops are bad!
Exiles have no good 1 or 2 drops. This is just the reality we live in. The same way Sleepers only have 2 drops, Exiles only have 3 Drops and some decent 4 Drops but for the most part their 5+ Drops are going to be your win conditions. So then what is the problem? Well if you are going to be playing 5-7 Cost cards on Turns 5-7 then when exactly are you going to be using Yagron,
Much like the Sleepers we have a decision to make. Play this Cresil/Hellbringer/Decension/Hungry Abomination etc... Or use Yagrons ability, which will leave me with 3-4 resources and nothing meaningful to play... The choice is simple, and the process continues. As the game goes on not only does an 8/8 for 2 cost mean less and less, but once again you have FAR better alternatives and thus less incentives to use Yagron's ability.
And this isnt a HUGE! Deal, atleast not as big a deal as Zomborg need a cost change (Atleast Yagron is still playable, Zomborg in my opinion IS NOT PLAYABLE
). But it is a Quality of Life change that I think needs to be made. I would propose this change:
Change Yagron's Active Ability cost to . Make the Demon it Summons have an Exile Cost of . So this way the overall cost of the Combo itself is still the same. Yagron then becomes a viable option for discarding cards and since Exiling a card normally gives you a resource benefit of  resource, Yagron's ability costing  keeps things balanced. This change will make Yagron stronger for sure, but I do not think it would make him broken, furthermore he doesnt price himself out as the game goes on since he can be used in conjuction with power 5-7 drops.Cards sitting in your hand is bad
Not much here, as an Exile the less cards in your hand the better. Tygrugh the Insane, Demon Wastes, etc... When you have something that gives you alot of cards as an Exile player, what you are essentially doing is limiting your play style options and making your deck one dimensional.
Granted there is some synergy with Hungry Abom, and making his Active Cheaper could make this spammable. But at the end of the day it isnt hard for me to make my Hungry Abom 60+ power as Yagron is now, I dont think giving me an extra 2-3 Demons making Hungry Abom 80+ is going to make a difference. If they dont have hard removal then they werent going to answer the Abom either way.
So yes, While Yagron does give you some benefit as far as discard goes and giving you an 8/8 demon. It also has some set backs, which needs to be factored into its cost.Pay Attention to Resource Curve Lightmare
The last thing, and my main gripe with Lightmare, is that they dont consider resource curves sometimes. Sleepers have MAINLY 2 drops... So a 2 Drop legendary that is lack luster is never going to see play... Because of better alternatives. If Yagron was a Sleeper card OMG would he be good, THE COMBO'S YOU COULD MAKE!!! The SYNERGIES!! OMG!! DISCARD A SLEEPER OF AVARRACH, GET A 4/4 ZOMBIE, INFECTIOUS TRANSFUSION OMG!!! But in an Exile Deck he feels clunky, the resource cost feels weird and doesnt synergize with the faction. The thing he gives you is ok but it isnt needed or wanted. He feels like a means to an end.
The same goes for Zomborg. In a Sleeper deck he is overcome by better alternatives that gives you more sooner and for no risk at all. If Zomborg was an Exile Legendary... OH "M" GEE!!! He would be in every command zone, you wouldnt mind sitting him in your support zone because Exiles are a slow paced faction anyways, they pick up at around Turns 6-7 as oppose to sleepers who are at their best at around Turns 2-6... Its all about timing.. making cards that arent just good, but are good at times when they need to be good.
Idk... But thats my take on all of this, I hope it wasnt too long.