Game with all expansions is massive.

I guess most campaigns were designed and tested only with core game and that expansion, so adding so much could easily destroy the balance.

I think that there are three things that mostly change the balance:

1. Plot decks.

2. Rumors.

3. H&M collections

So Plot decks just add power to Overlord. You may argue that fortune tokens might be good for heroes too, but it's always OL choice to give them to heroes in the first place. And you could alwasys take Trystaine deck and use only base card, which doesn't give anything to heroes. Personally I like the idea, cause there are times when you as OL can't win a quest, and ability to gain threat tokens just add secondary objective (like gold for heroes, though gold is much more usefull).

There are different kind of Rumors (with or without quest). First type helps the Overlord, second type can help both. But too many side quests lengthen the main campaign.

H&M collection adds a lot to both sides, that's true, But monster quality is really good and you can only use 4 heroes and ALL monsters from these packs. So this helps OL too.

With this in mind I want to discuss some things

1. Do you use plot decks? Why?

2. Do you use rumores? Why?

3. Do you use all H&M packs? Why?

4. Are there any overpowered/underpowered heroes/monsters/plot decks/Ol cards? Which one?

I'll address number 1: No, we don't. Without plot decks the heroes and OL usually have both wins and losses. Some campaigns go OL, some go to the heroes. When we used plot decks, a few things happened:

1) OL won a lot more frequently

2) Heroes got a lot more frustrated (before the 'whining heroes' response, I experienced this as the OL and ad a hero).

Some of this can be chalked up to increased OL power and options, but some of it resulted from many abilities to keep track of. For example, the heroes would attack a monster and forget that I could increase his defense by Alric's Armor of Darkness AND/OR by discarding an infection token, and now killing that monster is a much more daunting task than they had anticipated.

Plot decks do not always cause these problems- but we experienced enough of it in our group to sideline them as a general principle. Saves money, too.

The efficiency and power of a plot deck is highly variable depending on which one you decide to choose. As you gain experience with the game, you will likely find that the heroes will be winning more and more often than before, and to remedy "balance" you will find these plot decks to be a welcome addition to your arsenal. I would recommend not to play with them for your first games and introduce them gradually as heroes start picking up the game.

Don't forget that you have other options than ignoring a deck or deciding to play with one. You can choose one and only use the base card. You can deliberately ignore the purchase of some more powerful cards just because you feel the game is at its best balance power-wise between the two sides. You can let cards lie on the table without actually activating them. I think plot decks are a nice way to adjust balance whenever needed. I have almost never seen a plot card net me a quest. I´ve had decisive moments where a plot card was key to executing a sequence of play, but it was mostly backed up by OL cards or a specific type of monster. Never a plot card alone.

Rumor quests are a subject of discussion among the community. I personally think they give too much advantage to the heroes. I would never play one myself unless the gain was great and more or less garanteed.

H&M packs gives the OL more monsters to choose from, but also more monsters for the heroes to fight against. My hero players may be on the marginal side of the community but they always welcome new and fresh additions to the game in form of new monsters to toy with. Balance wise I think you exagerate the power of these packs. Sure, Kobolds are a big deal, Crow Hags are still under discussion too. Otherwise everything seems to be fair. The base game monsters are very powerful themselves so it's not like they are outdated by the H&M packs, on the contrary.

I always play with plot decks as they give a theme to the role of overlord.

I think the only overpowered cards around are on the heroes side, luckily they are not many of them. Crossbow, Logan Lashley and a few other weapons come to mind.

I should add to my seemimgly strong stance against plot decks- relatively recently, my playgroup changed- we lost a few members to new jobs and gained a few more. Therefore, I had more experience as an OL than a couple of the hero players had, and that definitely affected our inclusion of plot decks. After a few more campaigns, we may bring them back in.

Don't forget that you have other options than ignoring a deck or deciding to play with one. You can choose one and only use the base card. You can deliberately ignore the purchase of some more powerful cards just because you feel the game is at its best balance power-wise between the two sides. You can let cards lie on the table without actually activating them. I think plot decks are a nice way to adjust balance whenever needed. I have almost never seen a plot card net me a quest. I´ve had decisive moments where a plot card was key to executing a sequence of play, but it was mostly backed up by OL cards or a specific type of monster. Never a plot card alone.

Well, we do something like that. We like to try new/rarely used hero/classes, and in return OL choose his Plot Deck trying to balance things out.

We played SR with Splig deck and heroes won all 9 quests. Then we played Nerekhall and I used Merrick. I won 9 out of 11 quests, but I think that I would win it without plot deck. Same happened in MoR with Ariad. But last time we played LoR and our OL used Trystaine (really powerfull deck). Almost all quests were so close and sometimes just 1 roll of a dice or 1 mistake lead to lost. And Trystaine deck really helped our OL and made this campaign so great.

Tristayne's deck is one of my favorites too.

But honestly, a plot deck shouldn't normally be the key to winning quests at all. I am aware that you can chain some of Tristayne's plot cards since they cost you 0, which in turn adds up to the bill when you think retrospectively about what made you win an encounter, but it still cannot be the decisive element in your success. The problem in that case is more the fact that D2E is articulated around dice rolls (and card draw). Bad rolls set you back a lot, and good rolls increase your position drastically. It's a reality. So in clear, it doesn't matter if you add two damages to a succesful attack from a plot card, the issue is that this succesful attack shouldn't actually net you the quest. Abilties allowing you to re-roll some of your dices are therefore very powerful compared to effects that do seem nice but only increase an edge you already would get anyway.

Mainly, the heroes know you have these plot cards and when you are expected to activate them. They cannot counter a plot card, but they can dictate your play in numerous ways. They can trap you in a situation when you´d think best to play a card while it's not, or to spend the threat on something just so you cannot afford playing the real threat. Obviously 0-cost cards are trickier to handle, but they can still force you to exhaust it so it cannot be played elsewhere.

I´m not saying heroes can always counter your plot cards, or that plot cards are meaningless as they don't affect your odds of winning overall, they do sometimes, but they shouldn't be the core of your strategy. To use a high-reward plot card efficiently, you almost always need to perform a sequence of plays prior to playing the card, involving monsters, positioning and OL cards. For instance, you can Shiting Earth the heroes, but it's only powerful if you can follow up with something to capitalize on the new position of the heroes.