What is the biggest myth of adv time?

For me, the biggest mystery is the Mushroom War. It ties most of the mysteries together. No hints have been shown but the Farmworld, Marceline (who doesn't even talk about it and Ice King. No one knows who caused but a few theories have been made.

As for Billy's status (he's died), who made BMO (I've seen alot of BMOs in "The Real You) and how did Jake and Lady have babies (I have no idea O.o). I don't think they have much significance in the story as the other mysteries.

finn's identity. Who's her mother? Father? How did he survived the mushroom war? And another. How did the people became mutants or immortal after mushroom war? Did a bomb do it? did ice king/simon did it? Man, I hate thinking!

what happened in the mushroom war

My Biggest Question: Where were Marcelines parents the first 10 years of her life?

Is Susan Strong a Human or a fish person?
Where did the Lich come from?
Who was the Ice King? (Before Simon impersonified him)
Why is the Ice King so Crazy? (Before Simon impersonified him)
Who fought in the Mushroom War?
What happened to Betty?(Simon/Ice Kings fiance)
What happened to Finns parents?
Who destroyed the modern world with the nuclear bomb?
Who turned Marceline into a Vampire?
Why is Magic Man such a jerk? (He was nice before so said Lincoln)
Why did Lincoln know Death?
How was Lincoln even alive?

....And much much more...
(Sorry I didn't spell check, too lazy)

For me, it's Finn's background. What happened to his true parents? How was able to survive a war that happened 1000 years ago? How did one simple bomb change the entire world?

Mine is were the creators of the show really on LSD when they made Adventure time? My ex bf said they were...

My top 1.5:

Will Finn and Jake meet Fionna and Cake?
Is Finn the last human alive?!
(Please understand..)
...

The biggest myth for me, which I thought about recently (its too good not to share it) is: what if the land of Ooo is a mutated remnant of previous human life. my reason #1: in the episode "James" they travel through a desolate land with broken skyscrapers and a bridge. #2: later on, they arrive at a crater and James says "I'll prepare the radiation suits." this gives me the theory of a nuclear war. #3: Finn is the last human. #4: When the goo monsters come, and finn asks "what are those?" princess Bubblegum replies with "... creatures from another time." again giving me the theory of a nuclear war.