With the trap being laid out, I will first launch a surprise attack to the behemoth, if possible slicing his neck in one go, but I sincerely doubt it will happen as behemoth in general are a cautious monster and a king behemoth, I'm pretty sure it awareness toward it surrounding is high so my surprise attack might end up failing. After the surprise attack, I'll draw him out, toward the acid pit that is near the entrance hoping to dish out the maximum amount of damage there. With that said, I unsheathed my Scythe and imbued it in wind, light and thunder mana.

As the king behemoth are now in my sight, I'll activate my stealth mode magic as well, a spell under illusion magic. Slowly approaching the sleeping behemoth, this is it, as I'm about to land the surprise attack, his forefoot attack me! Looks like it manage to sense my presence even while sleeping, plus I'm using stealth mode magic, as expected of the S Rank monster, but not that this will hamper my plan. 

(You are still drowsy, so here you go!) [Ash]

With one strike, the Scythe land right In front of the behemoth eye, making the behemoth roar in pain, but I'm not done yet! With the thunder mana, I'll shoot all of my thunder magic right into it eye, before gouging the behemoth eye out. The Behemoth entered into an epileptic like state for a second but quickly recover afterward, so much so that it manage to block my second attack with it claw, and oh god, the claw is tough as hell! I can see that there are wound in it claw but I'm convinced it doesn't even suffer minor damage from it. The King Behemoth begins to launch series of attack by using both of it forefoot, such strength, if I keep fighting inside the cave, it will end up in disaster so let just bait it outside

With the acceleration magic, I lure the king behemoth while shooting light arrow magic, focusing on the wound to maximize the damage output, but it enormous strength and defense just shrugged it off like it was nothing. Not to mention it can keep up with my acceleration magic in such wounded state, this really is scary. 

(No doubt it pissed off right now, and it target is obviously me) [Ash]

And there's the first trap, with the momentum from the acceleration magic, I make a large leap forward, not even touching the icy layer and as for the behemoth, are you kidding me, it simply stomps the ground hard enough to shatter those ice floor! I do know that this trap will be useless to begin with but oh boy, it's disappointing alright seeing the trap that you set not serving its purpose, I mean the king behemoth doesn't even show sign of slowing down.

The second trap however, 

(It's working!) [Ash]

The king behemoth steps on the ground trap, the explosion per said doesn't cause that much damage but the spikes that hurl toward it at high velocity sure does. The spikes get stuck in between the foot as well as the wound, it even managed to damage the other eye as well. As we move toward the last trap, I noticed that there is many spikes laying around on the ground just behind the king behemoth (must be the spike that does not hit the target), and since those spike were part of my own magic, I control the spike as a group and attack the behemoth from behind, it works! But this just make the king behemoth become angrier

And onto the last trap, just like the ice floor, i make a big leap thanks to the momentum, and so does the behemoth

(This is bad!) [Ash]

Did the behemoth sense the trap underneath, or was it just copying me, either way this is bad! 

"Earth palm!" [Ash]

I make a massive palm using the cave ceiling just above the behemoth, putting massive amount of mana into it. The leaping behemoth do notice this attack, but there is nothing it can do now since it's in midair

BOOM

The King Behemoth are pushed down toward the acidic pit, struggling to get out but I'm not that nice . Light arrow, light sword, light bomb, all kind of light magic spell were thrown at it, and to maximize the effectiveness of the acidic pit, I even use mini tornado magic, so that the acid will cover the whole body of king behemoth. 

The King Behemoth, having enough of this, gather around a beam of darkness magic, and in an instance

"!" [Ash]

The blue sky? And that's the cave? Sigh... thank god I managed to use high grade light shield dome magic, even coating myself with earth metal magic to brace myself. Even that wasn't enough since I actually sustain quite some damage, and before I can even get myself up, that giant black of death leap upward, ignoring the cave ceiling and stand right In front of me, with darkness mana surrounding it body

"ROOAAARRRR!!!" [King Behemoth]

Such deafening roar, and it once again uses it claws to attack me, I can't dodge, not enough time. The direct hit from the enraged king behemoth sure make the right side of my body goes fully numb. Plus, I was tossed around 100 meters, it felt like getting hit by a truck

(This is bad, have to retreat) [Ash]

But my stamina and mana are at it low, even my knees are giving out. Is this it? No there have to be a way, come on, think! 

"Roar!!!" [King Behemoth]

It is rushing towards me once again, just think, think, think, think, think!

(Huh?) [Ash]

A powerful beam of wind magic attack the king behemoth from behind, and 

"You gotta be kidding me!" [Ash]

I mean, how come the two of us doesn't even detect those four? 

There are now four behemoths just behind the king behemoth, this is an awful news! But, the wind behemoth and the two fire behemoth keep on attacking the king behemoth, while the water behemoth approach me before using a healing spell on me. Water magic do have a healing properties, not as strong as light, but still get the job done. The water behemoth seems docile, plus I have a feeling it is trying to tell me something

"Are you telling me to join the fight as well" [Ash]

"Roar!" [Water Behemoth]

I just take that as a yes, still with the remaining mana, what can I do... well, just calm down and think...

(That's the only way) [Ash]

As the four behemoth begin to attack the king behemoth one after another, I take this chance to imbued almost all of my remaining mana with light magic, hoping to take down the king behemoth in one strike

(come on, come on, come on!) [Ash]

I just need an opening! Please make it happen!

The four behemoth, try as they might, can't seem to turn the tide of battle around, they are all an A rank monster, strong without a doubt, but up against the S rank monster, even if the said monster were injured prove to be a difficult task. In fact, one of the fire behemoths have it jaw crush by the powerful impact of the king behemoth as it were trying to launch a fireball attack.

Things look bad, I can't depend on them to create an opening, in that case, I'll create one myself

With all my strength being put to my lower half, I make a huge leap up to the sky, and once the target in my sight, 

"EXPLOSION!" [Ash]

A large explosion magic, explode just behind me, creating a high wave pressure that propel me toward the now startle king behemoth, thank god it works as intended. The water and wind behemoth sees the opportunity and ram the king behemoth with all their might, flipping it over! 

The king behemoth tries to regain it postures, but it was too late! 

"HAAAAA!!!!" [Ash]

With the scythe piercing the muscle, bone, organ of the king behemoth in an instant, I can see the magic core of the king behemoth just beside it heart. Too bad, I have to destroy such valuable magic core, but right now, my life are more valuable, doesn't want to get a romantic dinner with god of death once again, but I can send you to the god of death with this slice! As the light imbued scythe slice the magic core, the king behemoth make the last ditch effort, it uses dark mana from its magic core to propel me outward, but too weak, I'll just have to create another explosion magic and

BOOM

The magic core destroy! 

Now time to get out from the thorax... Ughhh... I'll appreciate a shower and thank you water behemoth, seriously thank you. Why do I feel like this water behemoth have more common sense than most people

And once I'm out, the two fire behemoth spew out high grade fire magic, burning the corpse of the king behemoth, reducing it to ash. Too bad but understandable, even I am reluctant to sell the corpse of king behemoth, sure it will fetch a high price but if someone with bad intention get ahold of it, who knew what they will use it for. Necromancy? Drug? Endless possibility are there and I don't want to be responsible for it

After they are done, the wind and water behemoth keep on pointing their claw towards the cave, I see... they are asking me to come along. Well, they are docile, and I have the feeling the reason behind it are because of the claw that Behe spit out. Once again, I enter the cave, going back to the depth of the cave to find a portal, with some strange magic stone underneath it. The four behemoth simply pass through the portal... I have a feeling I shouldn't do that, instead with the last bit of mana I have, I put the magic stone into my item box, instantly deactivate the portal. Thank god or else who knew what will come out next. And lastly

"Sorry, just like the king behemoth, I'll have to do it" [Ash]

As I burn the head of the light behemoth, I offer my prayer to the light behemoth, promising to take good care of Behe. It's a one sided promise, but should be good enough and now

(I'm too tired...) [Ash]

I have to use the scythe as a walking aid, dragging myself, putting so much effort just to go back to the cave entrance... fuuhhh.... this sure is tiring and I don't even have any food inside my item box. Should make a note to myself for that, but thank god the adventure that were exploring the third floor came. For now, I'll explain what happen as one of the adventure carries me on his back