Hola Zana here with a new story (sort of) for you all, my sister and I put our heads together to find all the possible (and not so possible) endings of Detective Conan, so without further ado the endings!

By the by this is how Conan could turn back into Shinchi… or die… Yea.

The Most Realistic:

Hibara is able to come up with an Aptoxin based antidote that is not temporary. (This is the most realistic)

Conan has to get a blood test and scientists in the hospital find something wrong with DNA, scientists then find antidote. Hibara is not involved.

Conan requires some kind of organ transplant and the foreign organ brings him back to himself.

Doesn't turn back… OVA 9 story. So he stays Conan and Ran lives a desolate life finally giving up on him and marrying a doctor.

Black Organization has antidote and after defeating them finds the antidote, returning to himself.

Ran finds out Conan is Shinchi, knowing there is no hope for him to return to his normal self she takes the Apotoxin too, leaving them to grow up together (again).

Disney-type Endings:

Conan gets a true (not lifesaving) kiss from Ran and returns to himself.

Dies but ran cries on him and he revives, and he is Shinchi.

He gets a fairy Godmother that turns him back.

He defeats the Black Organization and like magic he turns back to himself having defeated the people who turned him into Conan no longer having power over him.

Conan tells Ran the truth of him being Shinchi and the truth sets him free (AKA returning to himself)

Conan discovers that he simply has to believe his Shinchi despite his circumstances and he turns back into himself. (Believe in yourself Conan, Believe!)

Soap Opera Endings:

Conan dies and in the course of dying he returns to himself, only to be seen by Ran.

Shinchi finds that he technically died when he was hit in the head and in dying in his 'second life' he returns to his first one, still alive with little time passing (Narnia time warp).

Conan finds out that Kaito is his identical twin he gets a blood transfusion in which he was able to turn back into Shinchi however now has thieving tendencies (like Kaito) and is no longer able to be a detective.

Shinchi finds that he has been in a coma for the last 3 or so years and that all that happened in detective Conan never actually happened.

Conan finds there's a company in America that finds antidotes to poison, so he tells Ran the truth and moves to America while trying to keep a long distance relationship with Ran and every girl he meets falls in love with him as Conan and finally returns to Japan as himself, with some relationship problems to boot.

Sci-Fi Endings:

Professor Agasa creates a transfer machine where it transfers Conan's problem to another person, Heiji sacrifices himself to get Shinchi back to normal and back with Ran because it's well known that Heiji still doesn't know Kazuha likes him and sees no reason he can't take the fall for 'Kudo'. So Hejii then becomes the little kid and Shinchi the teen.

Dr. Agasa develops a mechanism that allows Shinchi to turn back into his normal self with the switch of a button and without the use of an antidote to the drug he was given.

A time paradox takes place switching him with his childhood self yet keeping his remaining brain intact. The pill he was forced to take was not a chemical but a time travel pill. The moment Haibara creates antidotes actually rips in the time space continuum allowing his old self to reurn but only for a short time. Once this is figured out Shinchi trapped in a time space continuum he is replaced with his 'teen self' and all goes back to normal.

The moment that Shinchi is given the pill a rip in space time forms making him live 2 parallel lives, one in which nothing happens and he continues on living as Shinchi and the other the one we see on the show. Once that Conan deducts that he is not getting anywhere because the Black Organization is not getting weaker but staying the same despite his efforts, he discovers what happens and instructs all around him to recreate the day and by living the same day twice he sews the rift in the space time continuum together with his duel life having memories from both lives.

creates a time machine, Conan/ Shinchi then prevents himself from getting hit in the head, taking the drug and turning into Conan.

Shinchi is trapped in a sort of videogame by the Black Organization trying to test Shinchi's detective abilities

Endings involving other characters being bad guys:

Haibara has been giving Shinchi doses of the poison every day since he was originally poisoned, focused on keeping him away from Ran and the Black Organization. Once he finds this out he put a stop to this action

Mori is actually an evil genius intent on stopping Shinchi who has been hindering his detective business. He created the Black Organization from his Mahjong friends to keep him occupied from stealing his glory as a detective. He was the one who poisoned him in the first place and has the antidote. Once Shinchi finds this out he tracks down the antidote and returns to himself.

Shinchi's parents gave him a 1 year active drug to test his detective abilities. It is supposed to wear off 1 year after it is given to him however he got himself in a predicament caused by an unexpected independent stimulus, the Black Organization. This causes him stress and causes him to stay drugged longer than expected.

Ran works as a Black Organization member and is in charge of giving him drugs night after night to fulfill her job as a Black Organization member. She pretends to be in love with Shinchi to throw him off her case. Conan figures this out and puts a stop to the problem.