Here it is:
Chapter 1.
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The grasslands are peaceful, secure and safe thanks to two guys (or one human and a stretchy dog?) who kept evil out of the Land of Ooo.
But something is going to happen and shiny things will make them flip out.
~
An Assassin insignia on a page of the simulated Enchiridion surprised our two heroes.
"Finn, why is the other page blank?" Beemo asked. (A/N: Only the guys who have the so-called "sixth sense" can read it btw)
The human boy focused...

Jake and the living console had their respective auras, and Finn had whitish-blue.
"Bro, what can you see?"
"Uhh, a glowing sphere with tech stuff."
...
"Let's go to Dad's Dungeon!" Jake exclaimed, stretching all the way to the stupid-looking rock.
~
Finn's POV
Jump, leap, run...
Jump down again, climb on steep cliff, find glowing hole.

I jumped down the hole, grabbed the chip, climbed up again, meeting Jake with the holo-viewer.

Pressing play was the most epic situation that I have ever experienced.

Writer's POV
"Hello Finn and Jake, Joshua here with Finn's original dad."
"SERIOUSLY?" Finn said in shock.
"We kept an Apple for you guys to take in Aaa." The blonde man with the hood
"Aaa? You mean Ice King's delusionary delusions?" Jake asked.
"You guys are entrusted with the power and the responsibility, so take it and hide away."
Joshua and the hooded man turned and said:
"We're out."
"Wait..." The boy said.
"What?" The hooded man responded.
"Are you really my dad?"
"Yep."
"Then what's your name?"
"Aureus Mertens, at your service."
_____________________________________
Finn finally saw his dad as a real Assassin!
What's with the Apple?
Will FnJ retrieve it?
What will happen?

TBC in Legacy chap 2: Earthshake, Swapmake!