Campaign challenges

[Inky]

Ah, I should have known people have already done HttT with every unit type imaginable! But I've been looking for an excuse to replay HttT, so here it is...

Heir to the Throne scouts/loyals only
(Credit goes to beetlenaut for the idea, and for already having done this.)

(version 1.12.4 hard difficulty, no saveloading, scout types + loyals)
It turns out you get about a zillion loyal units in this campaign so they do most of the work while a couple scouts act as distractions. About halfway through the campaign I have so many leveled loyals it almost becomes a regular playthrough (except with more gold!). There are some scenarios where I have to get a bit creative though. I found Princess of Wesnoth and Valley of Death especially difficult.

Scenario summaries

S1 The Elves Beseiged
2 restarts- first time Konrad died in an attempt to get him some XP (not recommended. he's so weak he should just run like a coward to the signpost). Second time Delfador got ZOCed and killed.
I manage to level a rider, and get a little bit of XP for two other scouts.

S2 Blackwater Port
I aim to get Simyr, so I send Delfador, Haldiel and some scouts southwest to wait for the dawn and strike the leader.

One restart. I was too scared of sending too many units SW and luring all the orcs, but I sent too little and Delfador and co. got stuck in the south due to not being able to kill the units in the way fast enough.
On my successful attempt I sent a whole ton of scouts SW and maybe I got lucky but they didn't lure too many orcs their way. I use a scout as bait to try to lure the orcs east. The leader foolishly leaves his keep on turn 6 to attack a scout and is easily killed by Delfador on turn 7.
Haldiel manages (with a bit of luck) to get 2 kills. Unfortunately Konrad still has 0xp, but this will be remedied in the upcoming scenario.

S3 Isle of Alduin
An easy scenario, excellent for XP gathering. I finally level Konrad to 2. No restarts.

S4 Bay of Pearls
I really would like to keep all my mermem alive, so I take them south onto land. The nagas follow onto 30% defense terrain and are quickly killed. Only when most of the nagas are gone do I send the merman back into the water.
Simyr has an extremely close brush with death and probably should have died, but lives to see another day.
I level Elrian into a white mage because I desperately need a healer. Even with the white mage from the next scenario, I think he is better off as a white mage, because another +8 healer never hurt.
No restarts. Finished turn 20/21 by defeating both leaders.

S5b Isle of the Damned
Since I don't have access to scouts (not that I would want them here) I recall only merman, the 0 xp ones being meant as cannon fodder. I send them all northeast to take out the lich during the next day. The lich loves using his ranged attack on mermen fighters, even getting in the water at dawn to do so!
I send Delurin to the temple to find the white mage, and both make a hasty retreat to Konrad's keep as I have no land troops to support them.

After I kill the north lich I send all the mermen south, some of them stopping briefly to heal. However time is short, as Konrad's island keep is being beseiged by the undead forces of the other lich. The south lich happily gets into the water to attack my Merman warrior - a fatal mistake - and I destroy him easily during the day.
I level the storm trident merman and the merman hunter to a netcaster, and another fighter to a warrior. I get lucky and all my cannon fodder survives, but it doesn't matter because I have more mermen than I will ever recall later.
Restarts: 1 because Delurin died. He visited the temple with the revenant first and when I tried to run away with him he got ZOCed by a ghost.

S6 Siege of Elensefar
One restart. I actually had an extremely good first playthrough (no losses)...until the end when I couldn't hit that stupid necromancer on 40% after I lured him out! So his newly summoned units got a turn and I ended up losing Simyr, Delurin and the loyal rogue. Maybe I should have sent a scout earlier to trigger his guards, but I figured it would be easier just to kill him before his guards could attack. While this usually works, I suppose it was my fault for leaving it up to chance.

Attempt #2: I lose 3 riders but all the loyals live. I trigger the guards and then retreat, killing them all for experience.
I basically hold the water line with the help of mermen. You get more losses this way than if you retreat to your keep during the night (since you're on 40% instead of 60%), but it's much faster and the turn limit here is very tight so it's probably the better option. I ask the thieves to wait until I take the city so I get an extra one.

S7 The Crossing
My impatience causes me to have to replay this scenario several times.
Attempt #1: I try to just recruit fast units and rush the eastern leader. It didn't work - I didn't have enough strong units to break through the line and I just ended up sandwiched between the two orc forces at night, not a good place to be.
Attempt #2: I stupidly chase units into the hills at night triggering a ton of ambushes, and lose one of the white mages. I should just stay out of the hills.
Attempt #3: Success, although I regret using so many scouts as cannon fodder - they can die to one attack at night and there goes 18 gold! I stay far away from the hills and form my line on flat terrain. I focus on gathering experience and kill both leaders, leveling many units in the process.

S8 The Princess of Wesnoth
I had a lot of trouble with this scenario - all those beefy loyalists would come at once and I just couldn't kill them fast enough. What finally worked was waiting in the forest in the center of the map, luring out one or two units at a time hopefully. Since I had very high income, I left Konrad in the keep and had him recruit one fodder scout per turn. Delfador was extremely useful here, being the only one who can really damage those high HP melee units.
2 restarts for the same reason: Kalenz died. He's really weak and shouldn't be on the front line. In my third attempt I'm even scared to put him on the front line when he is on 70%.

S9 The Valley of Death
One restart, I tried to rush the NW leader to steal his keep and recruit again there but it didn't work because the chocobones and wraiths were faster than me.

The second time I experimented with a pretty cheap strategy: recalled Delurin, the two mages of light, some outriders, the elvish hero (giving him the holy water so he can get some XP) and recruited fodder scout after fodder scout. Then I ran with everyone to the NW mountains, taking advantage of the fact that undead are slow on mountains and my units have high defense there.
The key to surviving in later turns was to try to move my units next to the walking corpses since they're weak, and hope my units don't kill too many corpses on the counterattack. I lost 8 newly recruited scouts.

S10 Gryphon Mountain
Since this is another easy level I recall the units I want to get XP for (e.g. the two thieves who are still level 1.) Annoyingly, the loyalists will attack the gryphons on their turn who will then immediately attack me every time! Luckily all my units survive. No restarts.

S11 The Ford of Abez
Recalled one keep of mermen and moved Konrad north immediately. Sea monsters mostly fought with Asheviere's troops, so it's some easy experience for the mermen.
One restart due to being too aggressive at night. It's best to just retreat out of range of the northern orcs and wait for dawn.

S12 Northern Winter
This map is easy, although a bit annoying as it's huge and a whole horde of wolves will come and steal all your villages. Fortunately scouts are the perfect counter for this. Due to all the scouts and loyals I get a massive gold carryover! No restarts.

S13 The Dwarven Doors
Three unsuccessful attempts. (First time: I thought it would be a good opportunity to gather XP since I had such a huge gold advantage but it made me run out of time. Second time: I recalled two keeps worth of troops but this turned out to be too slow - got stuck with Konrad in the south again. Third: Better (I made it with Konrad), but the loyal avenger died.)
I just recalled a keep of fast (7 MP and greater) units and ran north, using the middle keep to recruit delaying fodder scouts. Still, it's very close and I barely manage to keep the loyals alive.

S14 Plunging into Darkness (story only almost; I kill the spider and get the gold).

S15 The Lost General
Ugh, the beginning of the underground scenarios. I recall the loyal outlaws, two white mages and a couple outriders. I trigger the undead in the south and easily just kill them one by one in the bottleneck. A pretty easy scenario overall. No restarts.

S16 A Hasty Alliance
I recall my tankiest units (paladin, highwayman, grand knight) to survive the first assault; everything afterward is easy. The ally acts as cannon fodder for you. No restarts.

S17 Scepter of Fire
I dislike this scenario, with the randomly appearing lava and Saurian skirmishers, which are annoying as you can't really avoid them. Overall an extremely uneventful level; I defend the bottlenecks in the south while Lisar and Delfador go find the sceptre. No restarts.

S18 A Choice Must be Made
To kill the undead is trivially easy. Recalled my anti-undead units (two Mages of Light, the Fugitive, highwayman, paladin) and a few fodder scouts. The undead waste the night going after the scouts and are wiped out immediately. No restarts.

S19b Swamp of Dread
Surviving the initial wave of undead is difficult; I accidentally expose the mermaid priestess and she dies but this is the last scenario where merman are useful anyway. I give Kalenz the void armor since he probably needs it most.
One restart; underrecruited and got overwhelmed in the center.

S20a North Elves
I first head south onto the humans' island to avoid the orcs, then I head north again when the allied elves are distracting the orcs/humans. I barely encounter any resistance.
One restart: I tried to run across the center of the map but this isn't a good idea as the orcs and humans will both attack you this way.

(S21 Elven Council - story)
S22 Return to Wesnoth
The enemy has level 3 troops so a unit can easily die, but they only have enough gold to recruit a few meaning they are very easily wiped out.
One restart due to Lisar dying to all those Royal Guards from the leader south of Konrad's keep. Basically I tried to rush him, but I didn't have enough units to kill everything because I had planned to defend in the north during the day but changed my mind when I saw he only recruited four units.

S23 Test of the Clans
Once again I turn to the time honored tactic of cannon fodder scouts to act as bait for the charging knights and lancers. Killing 50 enemies is simple but I only manage to kill 2 of the leaders before doing so. No restarts.

S24 Battle for Wesnoth
Since it's the last battle I have a little fun and abandon any strategy, throwing my units recklessly against the enemy, losing a massive amount of units. This does make me have to restart twice though, as Lisar died once and Delfador died the other time due to being too aggressive.

I give the killing blow of Asheviere to a level 1 scout, a fitting end to this campaign.

Recruits: 97 Elvish scouts!
Losses: 103 total (35 in final scenario): 65 elvish scouts, 14 riders, 10 outriders, most of the loyals in the final scenario

[Aldarisvet]

Wow, intresting thread. I can add something about my campaign, it is full of challenges mentioned above and also with some original. Well, as I understood, above were discussed "voluntary" challenges, but in my campaign all restrictions are "built-in".
Scenario 1: You start with ONE level0 unit with 20hp, he is a main hero. You CANNOT recruit. But main hero have plague staff and can get zombie army from two goblin tribes which are fighting each other.
Scenario 2: More 3 heroes joins. Still cannot recruit, and cannot recall zombies from previous scenario, but that of them who upgraded in previous scenario from level0 to level1 joins automatically. But also need to fight versus orc poisoners.
Scenario 3: You can recruit all types of dwarves, but they could not be recalled later.
Scenario 4: You can recruit peasants and horsemans only, and only horsemans upgraded to lancers joins in next level. So again, need to get as much upgraded units.
Scenario 5: Can recruit only level1 Healer Mages (junior White mages thats heals +4).
Scenario 6: Can recall and recruit mages from previous scenario. The map is an ocean of forest and you have to fight versus woses and woses shamans. Thats means that your enemy is invisible before he attacks.
Scenario 7: Can recruit Saurian skirmisher (and recruit/recall mages still).
Scenario 8: Can recruit/recall Saurian skirmisher and mages. The map is an ocean of swamp and you have to fight versus lot of saurian mages with 4-7 magic attack and teleportation ability. They can jump from every village you coming close.

Restrictions with type of units you can recruit compensated by many heroes and loyal units of various types.

[beetlenaut]

About halfway through the campaign I have so many leveled loyals it almost becomes a regular playthrough

Yeah, HttT is not that hard with any one unit if you allow recalls. Especially after the halfway point. The hardest thing I've tried (and completed) is TRoW with only mages. (I have also tried TSG with no recruits at all, but I can't get to the second scenario with anyone left.)

I can add something about my campaign, it is full of challenges

The point of the campaign challenges in this thread is to do something unusual to make the campaign harder than the author intended. If the author intended it, it is automatically not this type of challenge.