Mold Earth was not a very mana intensive spell. It actually didn't exceed Felix's passive mana regeneration, nor even come close to doing so. Felix figured this was most likely why it was such a slow spell. There was probably a higher level version of it somewhere. Felix didn't know. He was knowledgeable after having been in this world for a few years, but it wasn't like he had time to do nothing but focus on learning magic. He didn't even know what his elements would be until a couple of days ago, so it didn't make much sense to try learning about all of the low and mid tier spells which numbered in the thousands, compared to other more practical information at the time, like the general state of the world, or how to run an orchard.
Therefore, he only knew about the most common peasant-grade or low-grade magics, and extremely famous spells, most of which were on the super high end, like Mass Hellfire, Meteor, Hurricane, etc. which were all spells he was unlikely to ever see in his lifetime.
Well, actually, he thought about it a bit, and he had suddenly become very likely to see them, since he was suddenly brought to the frontlines of the war between humans and demons right before a massive battle, wasn't he? Well, the military didn't give much of a care for him, but most likely the day before the battle they would pull him inside the fort and he would at most do some backline stuff like repairs. He wasn't trained at all, so if they got to the point where they asked him to be a fighter, that meant they probably already lost.
While he was thinking about this, Unit Leader Louis came over.
"Felix, was it? I know you probably don't think much of us right now, considering what you got thrown into right after arriving, but please understand the situation is just pretty desperate, so we didn't have much choice but to ask for your help like this. I don't know how quickly you regenerate mana, so if you run out and need to rest and recharge, don't hesitate to do so, no one will blame you. Here's an earth spell manual to peruse in your free time, if you get any in the near future. Keep up the good work." he said, while looking at Felix's progress and nodding. He handed him a spell manual full of low level earth spells. Felix thanked him and Unit Leader Louis ran off to check the rest of the unit.
Felix knew he was probably being a bit harsh mentally to the military. They were caught by surprise by the recent defeat at the battle of the Crimson Plains outside of the fort, and the capital blockade recently both happening one after the other. Assuming he didn't die horribly in the next week, the military would probably make things up to him, and they showed their goodwill by giving him a spell manual. Well, that was all well and good, but, it didn't change the fact that he was currently isolated and exposed on the edge of the fortifications while there was demons literally a mile away from him. Luckily, they couldn't really sneak up on him, since it was a barren clay plain between the two side with just one or two random trees and a couple of random shrubs.
However, a quick frontal strike was definitely a possibility. A demon metal mage could definitely cover that distance quickly enough and take him out before he could get any help. They probably wouldn't bother to do so because it wasn't worth risking a trained metal mage to take out some random untrained newbie earth mage like Felix, but Felix also didn't like the thought that the only thing keeping him from getting engaged upon was the fact that the demons figured it probably wasn't worth it and it was better to just wait for their main forces to arrive in 3 days.
There were human and dwarf forces on guard in the fortifications to be sure, they were everywhere, watching the demon vanguard forces like hawks, however that didn't do much to reassure Felix. The closest watchman to Felix was about 2500 feet away in a watchtower, and he looked to be a water mage, which made sense, since water mages were the best at investigation. However, they were nothing much in terms of speed, so, Felix didn't feel like he would protect him reliably.
The only thing Felix could do was rely on himself. He pretended like he was out of mana, and he began to rest for a bit, drawing in mana and earth around him. The water mage glanced at him briefly but then ignored him and went back to watching the demons. He assumed Felix was simply recovering his mana. In reality, though, Felix was working on spell construction, hoping to complete Fling Rock. He needed something usable in combat, and he needed it quickly.
Felix was quickly startled. Since he was right next to a mountain, and since he was connected to the ground, and no longer in a wagon, as well as the earth being his major element, his construction speed skyrocketed. He was completing an earth node every about 3 and a half minutes. Compared to the 10 minutes it was taking him to construct darkness nodes during the middle of the night for Night Eye, for example, this speed was simply incredible.
Felix "rested" for about 15 minutes, and worked on the trench for another 45 minutes. Then, he "rested" again, and finally finished constructing Fling Rock. He saw a small nearby rock, and used the spell, flinging it out into the plain as hard as he could. He wasn't sure, but it looked like he could get a small rock that could fit in your palm to move at about 40 miles per hour, and he could use it on any small rock within about 20 feet of himself, within any direction, and towards any direction. It wasn't a super amazing spell, but he felt a lot less naked now. Maybe he could fling a rock at a demon trying to murder him and he could flee a bit further when they flinched or dodged it.
The sun was going down now. It was already pretty late in the day when he arrived at the fort and got flung out here. He could feel the darkness element rising in the world. Felix noted most of the others from his unit returned to the fort, but he didn't bother moving. He knew he was to be out here for the night. He actually was making pretty good progress on his trench, he had depressed the earth about 2 feet in a line of 500 feet length in the 2 and a half or so hours he had been out here.
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Unit Leader Louis checked in on him quickly before he left back to the fort, gave Felix the backpack he had brought with him, filled with food (Mostly salted meat) and water bottles, and told him if he needed anything or saw any issues with the demon, to report it to the new night shift water mage on duty in the nearby tower. Then he left for the night, leaving only Felix, his trench, and the water mage in his watchtower, who looked at Felix once or twice when he first got to his station, then promptly ignored him and watched the demons.
Felix started using Night Eye when the sun went down, so he could see. He kept working on the trench, and sat down to rest every half hour now, since there was a new water mage watching him who didn't know his old resting pattern, and even if he did, he could use the increased mana drain from Night Eye as an excuse. It actually did have an increase in his mana usage, but as a peasant-level spell, it was still insignificant even when combined with Mold Earth. Using both of the spells together only took up about 15% of his resting, passive mana regeneration, he didn't even need to actively intake mana.
He browsed through his earthen spell manual to look for the next spell he should construct. Right now, he needed small and valuable spells to quickly increase his power, since he was in a dangerous situation. He quickly settled on the spell "Pitfall", which quickly opened up a small hole in the ground. He began constructing the spell framework immediately, spending 30 minutes to work on the trenches, and 30 minutes to pretend to recover while also building his new spell. The Pitfall spell was at the very lowest end of the low-grade, having exactly 100 nodes. It would take him roughly 6 hours of construction time to build.
Felix kept up his half an hour on, half an hour off strategy for 2 hours while keeping an eye on both the water mage lookout and the demons. The water mage had looked at him a couple of times during the first hour, but eventually he stopped caring about Felix. Felix then stopped caring about working on the trench and focused on spell construction. Unit Leader Louis hadn't even bothered checking how much progress he had made on his trench, because, as Felix could obviously tell, he didn't care about Felix, and did not have any expectations for him anyway. He probably didn't even expect Felix to survive the night. Hell, he probably handed him the backpack of food and water not for nightly provisions but because he expected him to flee in the night. It would explain why it was completely full of food and water instead of just having enough to tide him through the night.
Felix didn't think Louis was bad, since he had done at least that much for him, but he knew that the military had it's own concerns, and Felix just simply was not one of them - if he turned out useful, great, if he didn't, no loss to them, they didn't train him in the first place. And a couple of pieces of salted meat and some water bottles were similarly basically nothing.
What about the time and money they spent transporting Felix, and the rest of the people from Gurnkey? Well, the vast majority of the population lived everywhere except the southeast of the kingdom. Felix figured they probably only bothered going so far out of their way to grab them because of laws requiring each noble to contribute certain numbers of people. So it was only done out of those obligations, and now the military was focusing on getting people from the much more numerous and prosperous regions instead.
Regardless, Felix spent about 5 hours straight working on Pitfall, finished it, and then spent the remaining hour of the night working on his trench. The sun rose, and the rest of his team came out, and Louis came over, looked surprised to see Felix, and told him to return to the fort and rest, informing him that tomorrow would be the last day he would be outside working because the demon's main army was expected to arrive roughly the day after tomorrow.
Felix promptly returned to the fort, was let inside, returned to his room, and went to sleep. After about 7 hours, he was woken up, and told he had an hour to wash up, eat, and prepare before he headed back outside. He took the fastest bath he could, ate a good meal, and stuffed even more salted meat and water into his bag, and headed out, right back where he was yesterday. He greeted Louis, who gave him a simple nod, and he got back to work. He tested out the Pitfall spell he had constructed last night briefly. The mana drain was more intense than any of his other spells, but even so, it only took up about 3 seconds worth of his passive mana regeneration amount for pretty decent effectiveness. He used it and it did exactly as described, opening up a small pitfall, up to about 50 feet away from him, but it did so in under a second. It wasn't a spell that was going to wipe out any armies, but it's tactical usage was obvious. He continued working on the trench and pretending to rest, and began constructing a new spell, this time working on another cheap spell, "Sand Attack". Well, it wasn't much of an attack, actually, all it did was fling nearby sand or dirt into someone's eyes. But it was cheap and also probably pretty effective. It had about 90 elemental nodes in it's construction, putting it on the upper end of peasant-grade magics, and it's frame was in the shape of sand being tossed into an eye. Felix estimated it would take him about 5 hours to construct the spell.
So, Felix worked just the same as yesterday through the afternoon and evening, then Louis came over to check on him, and this time actually checked his trench, and looked pleasantly surprised that he had actually gotten quite a bit of work done. He clapped Felix on the back, and told him he just had to stay out for tonight, then he could hang back and hide in the fort from tomorrow and he would make everything up to him. Then he left and it was just Felix, the same water mage as last night on lookout, and the darkness. The water mage looked at Felix once, snorted, and watched the demons. Felix ignored him, put in 15 minutes of token effort into trenchwork, and then sat down and finished Sand Attack over the course of the next hour. He tried it out, and it flung a good amount of the nearby sand and dirt in whatever trajectory Felix wanted, but obviously it wouldn't do any damage to anything except for someone's eyes. Or maybe you could fling it into someone's open mouth, if that was possible. But Felix wouldn't count on it.
Felix looked over at the demons, saw no movement, and then was startled when the earth element around him started fluctuating, and the earth shook and knocked him off balance.