Higher levels cost more, on a kind of exponential scale that may vary by a large number of factors including the type of unit leveling, the type and number and levels of units croaked, and other activities involving the leveling unit's special abilities that may not even constitute combat. But the main thing is that you should imagine something like a logarithmic curve (not saying it literally is logarithmic), whereby low levels are achievable with a little combat, but levels above 10 or 11 become extremely difficult to obtain, and something like a level 20 unit is completely unheard of. Also notable is that not all of the numbers are available to the units and commanders to calculate, and so the existence of a predicable system of leveling at all is in the realm of the theoretical Mathamancers. Units cannot actually predict when they are going to level (Jillian is being flippant when she tells the Archons, "Cmon, it'll be fun. You'll level." but it would be a reasonable bet they might if they took out a stack of dwagons.)
You have to understand that the denizens of Erfworld don't see a lot of what a player would see in a game. Including XP. Leveling is a surprise to them, and XP (or the equivalent) is a theory (albeit a pretty solid one). The people are in the dark and guessing, and it's kind of hard to build an XP table by actually finding 10 new level 1 Marbits to croak, discovering that you level, then discovering through experimentation that you need to croak 50 to level again.
From a narrative perspective, the fudge factor is high. But that does not mean there is not one consistent mathematical system governing leveling. It's just opaque to the characters and readers at this time.
The general answer to your question is that power gains are linear and level requirements are exponential. It's not perfectly simple as all that, but to generalize, yes.
I would say the answer is d
, with the amount of XP awarded being a
. I doubt that c
grants XP. Different unit types may gain levels at different rates. A level 1 caster seems weaker than a level 1 warlord, but a level 10 caster seems more valuable than a level 10 warlord, so casters may level faster than warlords at lower levels and slower at higher levels. As Rob stated, it's a kind of exponential scale, so low-level units level faster than high-level units. Given her bonus to Decypted, Wanda may be level 8. If my speculation is correct, she is over 800 turns old. She reached level 4 when she was 25 turns old. Admittedly, she probably didn't have much to do at Faq other than hang spells on the tower, and that's assuming the tower never became full, part of the deceleration in her leveling may be the exponential increase in XP cost needed for each new level.
We know Countess Artemis took 640 turns to level from 6 to 7 through training alone, but she managed to level to 8 during the brief campaign against Haggar. That shows that combat definitely provides more experience than simply casting or training, but the later still provides experience. We know that Delphie "immediately" leveled when she started croaking Frenemy units, but Stanley said the uncroaked warlords would not gain XP for withdrawing from a fight. So there seems to be an immediate XP award for croaking units and an award for being in a victorious stack. We know that Parson has not leveled. He was in the hex and providing his Chief Warlord bonus when Sizemore was fighting Jetstone in the tunnels. We know that Sizemore leveled twice, although some of that XP may have come from kills made during the volcano link. Given the fact that over 2870 Jetstone units (that is how many Wanda uncroaked, there were others she couldn't) and 1875 marbits were croaked, it would seem likely Parson would have gained enough XP to reach level 3 if he got any XP. Since he didn't, there probably isn't a hex-wide or Chiefness XP award. Sizemore also leveled again from rebuilding cities, which indicates XP from just casting.
Wanda reached level 2 on her second turn. In that time, she had hung a spell on Minnow Tower, saw through the scouting veil, hit the Haffaton scout with haboken, been part of the stack that croaked the scout, uncroaked 66 infantry and 1 warlord and been stacked with the leadership during the successful assault on Goodfinger. By her sixteenth turn, she was level 3. In the intervening time, she had been involved in two field skirmishes, being wounded by a crossbow bolt in one, slain a copy cat with her staff, landed the killing blow on a roastbeast, reanimated several hundred corpses and 3 more warlords and been stacked with Tommy and her uncroaked during the successful assaults on Hamfurter and Frankburg. At this point, Wanda may have been well on her way to level 4. Wanda reached level 4 after another skirmish. She commented that she gained the needed XP through the combat and uncroaking. Given that the uncroaking would have taken place after the combat, it is probably what put Wanda over the top. Wanda also commented that she had spent little time training with her staff as a melee weapon. Hoboken does use juice, since casting it used the last of Wanda's juice that turn. As you mentioned, casting hoboken would have been less useful than using her juice for reanimation. The fact she didn't train with her staff as a melee weapon indicates there wasn't much need for it. Given this information, it seems likely that Wanda was not involved much in direct combat. The scout, copycat and roastbeast plausibly may have been the only times she directly engaged enemy units. Delphie was level 4 when Wanda popped, and Clay was level 3. They had seen precious little combat in their lives, and none since Wanda popped. They were casting the entire time, but neither leveled until Delphie started croaking Frenemy's air units. This would indicate that casting, while providing XP, awards it at a low rate. Since Wanda did not seem to directly engage in combat much, this would indicate the majority of her XP has come from leading a victorious stack.
As for the other units during the Battle of Goodminton, we don't know whether they leveled or not. Mack, level 4, and Cakes, level 3, were not in the same stack as Wanda and Delphie. They were stacked with the bastilla and archers. They would have gained any experience for the engagements their stacks won, but not from Delphie's actions. While Delphie's assault was impressive, she still croaked less than half of Frenemy's units and none of Quislings. Also, we don't know how the victorious stack XP works. Delphie was getting the XP for kills, so she was getting much more than the others. Wanda had just crossed the threshold to being level 4, so she probably has a long way to go to be level 5. We don't know what level Fritz is, but he is the highest level warlord Goodminton has, higher than Tommy. We know his bonus was enough to enable Goodminton to defeat the Haffaton force led by Larry, a level 7. It may be that Fritz needs alot of experience to reach the next level. As for Clay, maybe, like Wanda, he was just past the threshold of level 3 and had a long way to go to level 4. For all we know, Delphie may have been close to being a level 5 for a long time. Also, noting Delphie's increase in level was important to the narrative, since it increased the effectiveness of the assault. Clay may
have leveled as well, but it wasn't mentioned since it was unimportant to the narrative.
As for the exploit, Rob mentioned that there are modifiers to how much XP a unit earns. There may be something like a challenge rating from D&D. If you stacked a level 1 with 7 level 10s and had started hunting wild marbits, the challenge rating may be so low that the level 1 wouldn't earn any XP from being part of the stack, although he may gain it from units he personally croaked. Bogroll, a levelled twice for soloing Ansom, but he may not have gain any experience if he had been part of Wanda and Ansom's stack of heavies that took Warchalking. It may even be a double whammy. The higher a unit's level, the more XP it needs to reach the next level while, at the same time, reducing the amount of XP awarded for an action. Wanda may have gotten a ton of XP for reanimating every unit in the hex at level 1, but she may have gotten very little for doing the same thing with many more corpses in the tunnels beneath Gobwin Knob.
Also, some speculation regarding present Wanda. Wanda may not
get XP for creating decrypted. She doesn't use any of her own juice, and the Arkenpliers seem to be doing all the work. I'm not sure I believe this, but I thought I should point out the possibility.
So, my guess would be that Wanda gained a small amount of XP for casting the scroll, a medium amount of XP for being part of Delphie's stack, and a small amount of XP for reanimating Frenemy's croaked units afterwards.
This is, of course, just my interpretation. The only one who really knows is Rob. He does have a system in his head, although there is some narrative fudge.