With the compact, single boss layout of the dungeon, one single run isn't going to be enough to get Cain a level. Fortunately, he has Echoes available.
"I know how you two love a good competition, so I have brought you to another challenge. I want this dungeon cleared as many times a day as you can. Separately, of course. The exact details are up to you, and you are free to spice up the competition any way you like within those limits. Just give me daily updates on the score." Cain instructs them, and the Echoes give him the tentacle-wiggling Ancient version of a smile that keeps their teeth hidden.
That should keep a reasonable level of experience coming in. Not that Cain has a good reason to rush his leveling right now, but at level 290, he will be able to get the final skill in his Class Skill Tree.
[Ancient Horrors] Increase the quality of all Summons by 1 Rank and rename Basic Summoning Spells.
By the description alone, he can guess how incredibly overpowered that will be when stacked with his existing abilities. Plus, he will finally find out what happens when a Summon progresses past Ancient Quality.
Once that is complete, his next mission will be to find a way to obtain a fourth advancement class. Cain isn't sure that's even possible at level 300, but he hopes to find something not too long afterward. After all, he currently had the perfect class for it; he could grant himself whatever skill he needed to influence his progression.
That will require him to take a good long look at himself, though. Exactly what does he want? When he first arrived in this world, the answer was easy. He wanted the money and power to live a life that couldn't be called wasted.
That goal is pretty much accomplished though, isn't it? A castle, a Port, multiple Guild Houses, the title of Duke and rule of an entire valley, plus many lives changed for the better with his skills. Cain decides that so far, he's done a decent job of living up to those aspirations.
Going the route of Cixelcid and staying home raising adorable little Demonic babies doesn't sound all that bad either, but that's not a class. What would the skills even be? Increased virility? Maybe it would have advanced escaping toddler detection?
Cain wonders if that's a real skill because Cid could actually use it if such a thing exists. Maybe it is under the stealth detection category?
That keeps Cain's mind occupied all the way back to the Port, where he is ambushed and wrapped up by a hysterical Cyrene the moment he arrives.
"I thought you abandoned me. You were just gone, and I looked everywhere and couldn't find you, and I was so worried." The Lamia pouts, curling her face up against his chest.
"Did you think about messaging me to ask?" Cain asks, and the Lamia stops completely, the red and white patterned scales on her body reflecting the light like a Jade statue.
"Um, no?" She says quietly as Misha hides her laughter.
"How about you try that first next time before you panic? I just went out exploring one of the nearby dungeons and looking for more dinosaurs for Neffie. See, it isn't even lunchtime yet." Cain points out, petting her scales to calm Cyrene down.
"Sorry, I shouldn't have panicked. Did you find anything good?"
"A dungeon full of assorted dinosaurs at level 320. It's a short one, but pretty good experience."
"I know you can't take them out, but did you find raptors? Can they be ridden? Are they smart enough to be mounted?" Neffie calls, having run over the moment Misha alerted her to Cain's activities.
"The ones I found are bright orange and black, a meter and a half at the shoulders, big enough for smaller bodies to ride. They're brilliant and get very offended if you try to ride them. They're fast too, no horse could keep up with that." Cain answers with a smirk.
"Can you make me one? Maybe a Puppet one, not a Summoned one. Though a Summoned one might be good too, then I can call them later."
Cain calls out a group of them since they count as Lesser Golems, despite their incredible damage output.
Neffie cheers and shifts into a clone of Kone, calling out a group of them and hopping onto the back of the closest Raptor. The look it gives her is less than impressed, but as her summons, they don't attack.
Cain dismisses his summons while Neffie giggles and races around the town with her pack of Raptors.
[This is even more amazing than I thought. Everyone should have the chance to ride one of these giant lizards. Does anyone have a skill that can teach me how to use lances? Spearing things for the raptors to eat would be perfect.] She sends in Guild Chat as she races around.
That makes Cain wonder, the Goblin Cavalry [Bonded Mount] Summoning skill doesn't specify Mole Dogs, so could it be used to Summon Raptors if that's what the Summoner really wanted?
Cain makes a Puppet that looks like Neffie, gives it the [Bonded Mount] and [Charge] skills as well as [Knight combat Style: Lance], and then instructs it to focus on calling one of the raptors with [Bonded Mount].
The skill seems to hesitate for a second, possibly because it is a Puppet doing the Summoning, but the Raptor appears and nuzzles the Neffie Clone's face, allowing her to mount.
[Hey Neffie, I found the way to make your Cavalry without training living Raptors] Cain sends, and Neffie returns, followed by her pack, looking at the Puppet that looks just like her natural form.
"She can use a Lance and everything, but the only skills she has beyond the basic combat style is [Charge] and Summoning her Bonded Mount," Cain explains.
Even then, she will need a mana Totem nearby, as she might not have enough to charge after calling her Mount and has no mana regeneration. Still, that's enough for Neffie. She has shifted back into herself, which dismissed the summons and is giving Cain a pleading look.
"You can only have one skill added like that, ever. I'll make you a book for it later if you can use it." Cain laughs, petting her ears.
"No, absolutely not. No teaching my daughter to Summon Raptors." Lickity complains, pulling Neffie into a hug and glaring at Cain.
Neffie is about to point out that she can already do that because she's a doppelganger and can use other people's skills, but Misha silences her before the little Demon can say anything that upsets her mother any more than she currently is.