spoiler (may or may not be true cause i have the memory of a goldfish so take everything I say with a grain of salt)
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okay so like I haven't read the novel in a while but I'm pretty sure the egg a dragon but I can't remember if it's the Mc's brother's dragon or not and I don't know anything about if the brother is till alive since I stopped reading it
Lemme spoil you the thing that will hatch from the egg is an abyssal dragon that has it's past memories and that dragon was the former dragon of his brother that died. His brother (Heaven wing) is already dead but he is still looking for the spirit of his brother using the black king's set but his brother's soul ia still not in the abyss nor in the "in between" but rahter his brother's soul is inside the pocket watch that is why the pocket watch knows about almost the secret of every floors even though that heaven wing did not experience or gathered information about all that can be found in each floor. It is more like his brother's soul is still in an adventure in the pocket watch and reliving the old memories of it but using different paths to clear each floor
Spoiler warning
Don't read this, if you don't want to know.
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About the egg... It's a dragon. The Dragon is a reincarnation of Jeong-woo's Dragon (the same soul, different body).
About the brother... Jeong-woo is dead. The thing in the pocket watch is Jeong-woo's shedding, not a soul. Jeong-woo's soul is in a space (it's a space in the stream of Idea or something like that - he's not in the Tower) alongside with a soul of Jeong-woo's and Yeon-woo's mother. And their souls are frozen in time in that space.

Can someone tell me what will happen to the egg and if bro is still alive spoil me plsh