First off, is the XHeroes like, version 5 of the KHeroes that's generally accepted for online play, or are people still using KHeroes4? I haven't seen anywhere with data for the stats of XHeroes...

Also, are Stormheim units still the only accepted online additional units?

Finally, what's a good build for a set that uses Mercenaries? I've seen a lot of forum posts in the past on how to build non-Merc sets, but I feel like trying something new.

If I understand this game correctly you would want gnoll cavalry or assassins in slot 3 for mercenaries. You also want a warrior and probably also a barbarian in your set. I'm not sure what spot they should be in but I guess that depends on how important it is for you to get those mercenaries or not. I guess the rest of the set will focus on the usual negative bonuses.

The XHeroes are not officially version 5 of the KHeroes but unofficially I suppose they are. There isn't a large amount of differences between the X and K heroes. Mostly minor changes on the speed heroes (Thief/Barbarian) to make speed cost 3 points instead of 2.

And yes, the KHeroes tend to be used in PBEM games and the XHeroes in online games.

Stormheim is definitely the only accepted additional units. This set is an amalgamation of the NUT units and other extra army packs that were available at the time. They are the only units that are reasonably balanced enough to be used. All the other extra army sets are basically just useful for solo play or campaigns/limited set scenarios.

Note that even the Stormheim units have an online additional edit called the Troll units. Some players use those, some the original Stormheim units. The unfortunate part here is that the creator, Troll didn't rename them so you can't be sure which units you are using. I personally only use the original Stormheim units because I don't think the Troll edits were meaningful enough changes to bother making.

When you say you want a good set that uses Mercs are you looking for a set that contains a Warrior/Barbarian/General using renouned or you just want a basic set that uses Mercs?

KGB

Both, really. What does the Merc slots and strategy look like if I use a reknowned hero vs a non-reknown one?

Been forever since I used a pure renouned set designed to exploit the renouned power. Typically such sets are best used in team games (2v2) where you will get fewer cities/gold/armies etc so the renouned power becomes more valuable. Plus you have an ally who can focus on other things (like magic) while you focus on armies.

Assuming you are in a such a team game then it makes sense to put a really powerful unit in Merc 3 so that when you get them in quantity they pack a real punch. I personally favor Iron Golems or Balrogs. Both are cheaper than Elephants in terms of merc cost (the cost of mercs is based on their strength so a 6 strength Iron costs far less than an 8 strength Elephant). I think they are cheaper in terms of set point cost too.

For a non-renouned focus set that has mercs I am currently using the following PGS with great success.

Regulars
Gnomes
Archers
Banshees
Elf Calv
Gladiator
Battering Ram
Brass Dragon
Emerald Dragon

Mercs
Giant Rats
Dark Pegasi
Cyclops

Allies
Pegacentaur
Elephant
Balrog
Archon

Heroes:
KBarbarian
KMonk
KThief
KPriest

Mana: 12
Ship: Water Elemental
Mercs: On (as in I get merc offers at start of my turn. This costs 35 set points but generates merc offers about every 12 turns. Also allows the Barbarian to use his renouned skill). If you don't like this option you can upgrade to a Green Dragon in regulars or Halfling in regulars + Black Dragon in Ally 4.

The Giant Rats are handy in large masses from quests or from merc offers since they get the banding bonus. The Dark Pegasi provides a counter to all the Elf Calv, plus they fly and have good move ranges compared to Wights (which I used to use there). The Cyclops provide 4 hit archery immunity, good movement and of course trample.

The set is designed around fast movement of 20+ for all stacks (other than Elephants which I mostly relegate to defense). You can reach +5 in fear/chaos from the Barbarian or the Monks spells or items. The Thief provides the +5 siege should it be needed and in a pinch the Monk can get siege too. The Priest summons Archons which thanks to being in ally 4 can be move around in the fight order. The Archon of course combines with the Priest or Monk spells to give Morale +5. The Barbarian can also get Leadership if the Chaos is covered by Dragon + spell/item and a 2nd Barbarian can get +3 renouned for even more mercs.

The deadly killer hero combo is Barbarian/Monk which gets either Leadership or Morale +5 (or both given L7 heroes) + speed + acid + Fear/Chaos +5.

KGB

Wow, I didn't realize the cost of mercs is based on their strength. Is that a hard-coded thing or something?

What other sort of units are used in Mercs? I assume Slot 1 are spammable fodder, Slot 2 is some sort of support bonus unit and slot 3 = really meaty tank?

Some people use mercs to fit a certain theme in their set. You can for instance use it to fulfill your archery or assassin needs. archer elven archer moonguard. A friend of mine use it for herokilling units. Wich is exactly what that is. A favourite in slot 3 is assassin or gnoll cavalry. As you can understand there are some decent fighter units that you can have in slot 3 too. In my opinion the gold cost isn't that important but I guess I should do some math before I say something about that here

I did see a set where royal guard was used as merc2. I suppose that is a good thing if you like to have +4 castles

Yes, the cost of the merc is based on the merc's strength. By this I mean how much you pay to hire the merc, not how many set points it costs to have it in your set.

Here is the data on mercs and renouned.

CHANCE
Normal Merc Chance: 8%
Chance with Renown operating: N*8%

FREE
Chance of merc's being free: 5%
Chance with Renown operating: 5+N*2%

TYPE
Normal: MERC1:30% MERC2:40% MERC3:30%
Renown +1: MERC1:20% MERC2:40% MERC3:40%
Renown +2: MERC1:10% MERC2:40% MERC3:50%
Renown +3: MERC1:00% MERC2:40% MERC3:60%
Renown +4: MERC1:00% MERC2:30% MERC3:70%
Renown +5: MERC1:00% MERC2:20% MERC3:80%

COST
Cost is based on the strength of the Mercenary unit (from 1 to 9)
When 'n' units are received, the cost is (n*cost)
Normal: 10, 15, 20, 50, 100, 150, 200, 250, 500
Renown +1: 5, 10, 15, 20, 50, 100, 150, 200, 250
Renown +2: 5, 10, 15, 20, 50, 100, 150, 200, 250
Renown +3: 1, 5, 10, 15, 20, 50, 100, 150, 200
Renown +4: 1, 5, 10, 15, 20, 50, 100, 150, 200
Renown +5: 1, 1, 5, 10, 15, 20, 50, 100, 150

So you can see that when you have renouned +5, a 9 strength merc costs 150 gold each while a 5 strength costs 15 each. Thus it makes sense to never have mercs with a higher strength than say 6 which at renouned +1 cost 100 gold and drop to 20 gold at renouned +5. Assassins at 1 strength and 50% assassination are by FAR the super cheapest option in Merc 3 since each only only costs 1-5 gold regardless of your renouned level.

KGB

not much to add except that heroes need to be in a city at turn start for renown to work

Wow, is there anywhere "hidden" information like that can be found online? I want to know stuff like how army set scores are calculated and why Dragons have such inflated costs and stuff.

Okay then, so, I assume a set which doesn't use Warrior/Barb/General for Reknown just uses the mercs slot to fill in gaps by getting them from quest rewards and turns off the Mercenaries option?