The Normal, Grass, Water, Fire, Rock, and Fighting worlds make you fight the gym leaders and elite 4 members of that type before fighting HIM.
Beating worlds unlocks more worlds, and once you've beaten all 23 of them, you unlock the Dragon World.
Going through the Dragon World, you fight Dragon HIM just like you fought any other HIM form.
However, after beating him, instead of returning to HIS world, you get sent to yet another nightmare dimension.
It starts off by having you fight the Mariache Brothers, who use a bunch of Mexican Pokemon like Ludicolo and Muchoshot.
Then, they all die for no reason and a plant approaches you.
The plant makes you fight more creepy Mexican Pokemon, like Lunaticolo and Amigoggoth.
Then, you go through a short maze where at the end, you have to fight a battle against a guy who talks about eating and uses a bunch of food Pokemon.
After that, you are sent to a corrupted version of Surfin City.
There are a bunch of swimmers chasing you who say creepy stuff.
When you get to the truck, the swimmer tells you that all of their dreams will come true, and then she battles you.
She only uses a Phione, but then you have to battle some Pokemon called Doomsay and Doomsday.
After that, you are sent to a black void.
In the black void, you meet an Elias ripoff.
He had a tragic backstory, then HE gave him guidance, now he needs to strike you down.
However, this "tragic backstory" is about his parents getting killed by a banana tree.
Now, his only goal in life is to destroy bananas.
You have to fight him, and he only has one Pokemon: Catnobanana.
It is a pretty annoying battle since it sets up hazards then spams Whirlwind, but just use Toxic and you will be fine.
After beating Catnobanana, you are transported to what appears to be Mars.
On Mars, there is a PC for you to heal your Pokemon with.
There is also a Nicer who you need to battle.
The Nicer tells you that he is Marsech, the last living Martian, and one of HIS strongest servants.
Marsech was the one who brought HIM to Mars and sacrificed everyone, and now, he is going to kill you.
Then, Anne and Zaydolf arrive, and they're going to help you escape.
Then, you can choose Anne or Zaydolf as your partner for a double battle against Marsech.
Marsech uses 10 Pokemon, all of which are related to Mars in some way, one of them being Marsech himself.
After Marsech dies, HE appears.
HE is had enough, and he attempts to fight you in an unwinnable boss fight like he did previously, but the fight is not that hard.
The Eldcraftian only has Twindeath, which, while strong, is not an increased priority move, meaning you can knock out the Eldcraftian by outspeeding it.
There is also a Cryongi who you fought during the school segment, and a FEAR Magnemite who doesn't pose much of a threat.
After beating HIM, HE tells you that he's had it with fooling around.
The final two worlds, Divine and Chaos, are the hardest ones, and he taunts you to just try to beat them.
Then, you return back to HIS world.
At the top of HIS world, there is a portal.
As it turns out, HE made false versions of the 8 gym leaders and brought them from his worlds in order to stop you.
But Anne and Zaydolf brought the true versions of the gym leaders, and they will not let the false leaders stop you.
Then, you get transported to a hallway, where you have to fight each false gym leader in a double battle where your partner is the true gym leader.
False Crost proclaims that the world should be frozen, and Crost tells him to chill out.
False Lomar wants to cook everything, including humans.
False Claire wants to "punish" you.
False Vlad wants everyone to die, and Vlad tells him that he's soulless.
False Duette goes on a violent rant, and Duette tells her to balance her emotions.
False Jeeve Stobs claims himself to be above everyone else, and Jeeve tells him that that way of thinking is idiotic.
False Hiroshima wants to crush all the Juvites, and Hiroshima tells him that that is dishonorable.
False Merlin says that everyone is corrupted except himself, and Merlin tells him that there are still good people that False Merlin has not met because he isolates himself.
After that, the gym leaders tell you to finish the story and defeat HIM.
The final two worlds, Divine and Chaos, are able to be challenged.
These worlds look like heaven and hell, respectively, and they're also the only places where the Nicest trainer class appears.
In the Divine World, HE proclaims that humanity has committed unforgivable sins, and HE will deliver judgment.
HE uses mostly Divine-type Pokemon, but also Gigasvyre for some reason.
Divine HIM is an angel, who looks like a mix of a dominion and a cherubim.
In the Chaos World, HE says that humans are wild beasts pretending to be civilized, it's easy to revert them to this primal state, and that HE will consume everything.
Chaos HIM is a demon with 3 heads.
After beating both Chaos and Divine HIM, you can continue on to the final boss.
There is now a portal between the entrances to Divine and Chaos Worlds.
Going through it takes you to a boss rush, where you have to fight bosses from the "fallen timelines".
You have to fight Jirachi, Manglo, Gowen, a corrupted shoggoth, Lunar Guardian and all of his body parts, Corrupted Sol, Nameless Demon, Elias, Alphanne, and Mecha Zaydolf.
After that rush, you enter a hallway of self-reflection, much like the one before you faced Zaydolf in the Purification Camp.