On his way back towards his core room he wondered "if the boss monsters revive with their full memories, then doesn't that mean that they will continuously improve over time? hmm... I think I will have to keep an eye on the bosses combat abilities so they don't get too powerful for the floor they are on", just as he finished that thought he arrived at the core room then looked to the back wall furthest from him.

After concentrating for a moment the back wall disintegrated, the falling stone dust revealed a luminescent stone several sizes larger than his core that glowed a soft blue hue, Lucifer has had all his floors dug by ants instead of doing it himself and all of his monsters except the bosses are able to breed to repopulate, this saved him from using his own mana, causing the dungeons upkeep coast to be near zero, so he saved any of the access he could not store directly inside his core in this oversized mana crystal.

If any mage's in the continent learnt of the existence of this crystal there would be fierce wars fought over its possession, normally mana crystals only grow slightly larger than a fist before splitting into multiple separate crystals which then absorb the mana instead, however, since Lucifer is a dungeon he can artificially create any size crystals he wants and with the abundant mana of a dungeon feeding it, the amount of power this stone possess would put any Archmage to shame.

Lucifer had filled it several times and considered creating more crystals to hold his spare power, but he found when he used multiple crystals the surface area allowed the mana to radiate out faster because the crystals were not a perfect storing system, so he simply increased the crystal size every time it became full and when any mana leaked out his core simply absorbed it and put it back in creating an almost perfect cycle of mana.

Originally he planned to use the mana on something amazing when he had the chance, like some sort of indestructible boss of some sort, but the Eathmails he received thus far did not contain anything powerful enough to warrant such an amount of mana so the crystal sat there unused.

Now, however, he had a need for the power he should have used before to better defend himself, tendrils of blinding light emerged from the crystal as Lucifer refilled his mana reserves from when he was repairing the dungeon, then only a thin line of mana linked the two stones as he left flew away.

With his mana restored he begun creating better defenses, first he added more trapped hallways, he added them sporadically on the path to his core, someone may be able to disarm or negate his traps with magic once but they may not be able to after drowning in a swarm of ants.

He made sure to add sufficient traps to prevent someone from just flying through the rooms then began work on his creatures, the variety of ants was too limited causing them to be ineffective against a portion of the enemy's, Lucifer could not think of any way to have them defeat the mages barriers, however, he could think of ways to attack the supported warriors.

A case of literary theft: this tale is not rightfully on Amazon; if you see it, report the violation.

First, he added a species of ants that had sacks of acid inside their heads, they could not spit it and they required more food to regenerate the sacks that held the acid, but they look exactly like the normal ants so when the adventurers attack these ants their weapons will start to dissolve and break faster.

Second, along the lines of head mounted weapons, he added a small fire crystal just behind the skull of a small group of ants, these ants would require a longer time to mature because some of their mana would go into filling the fire gems, however, once their gem was pierced or destroyed they would violently explode, the explosion  would likely kill more of their allies than enemies, but Lucifer had never run out of ants before, however, to offset the friendly fire problem Lucifer modified the back and sides of the skull to be thicker to potentially direct most of the explosion towards the front.

Adventurers with a keen eye would be able to tell these ants apart from the slight difference in the shape of their skull and mages would be able to feel the ants fire magic coursing through their bodies, so adventurers may learn to avoid such an attack by attacking the body instead, Lucifer thought for a moment then decided to add muscles around the crystal that could break it when the ant willed it causing him to chuckle a little at the thought of little ant ackbars.

while he was in the long process of modifying the ants he went around the path to his core creating stairs, slopes small cliffs and other obstacles, Lucifer noticed that most mages were rather old and weak physically, so he added lots of stairs and small drop offs and ledges to tire the physically weak into exhaustion and hopefully cause them to make mistakes, or if Lucifer is really lucky an old archmage might just trip over and die on the way.

Meanwhile, a week had passed during lucifers renovations and outside the arcane university stood guard outside the dungeon, finally, Merlin could no longer deny the possibility that Jacobs was already dead, the fact that the dungeon did not go insane and spew out demons gave some measure of comfort to Merlin.

He called for a meeting with the other mages and discussed the next strategy to deal with the situation, they decided that it would be best for Merlin to go in alone to search for the rogue Archmage, he had the best chance of killing him and if Jacobs somehow got past him and had the core in his possession then the rest of the mages would be required to stop him.

Merlin called for his disciple and the pair entered together after passing through several barriers created by the mages, his disciple asked "if this is a trap set by Jacobs then wouldn't I just be a burden", Merlin chuckled then thoughtfully replied "even if it is a trap from Jacobs I would still win even with you accompanying me" then his expression darkened as he continued "besides I think he is already dead"

Ahri looked at him with surprise evident on her face "This is a new dungeon how could he die so easily in here, there are only 3 floors"

"Not everything is as it seems, besides this is no young dungeon, it was only "discovered" recently that does not mean it is young or helpless" replied Merlin

Ahri thought deeply as they walked and could not understand her masters meaning, unable to contain her curiosity she finally asked "what makes you think this dungeon is different"

Merlin gravely replied "this one is conscious" to the exaggerated surprise of Ahri.