I got some theory of mine.(it was translated from rus, so don't be confused pls)
In general, Guster is good because he did not allow war and did not allow a cold war between humans and monsters.
Guster created Delta after Ander.
because he realised that even Pacifist wasn't the best outcome.
After all, the monsters had somehow made it through the terrible grief, and even if Guster himself came and opened the barrier or saved Chara.
That still doesn't undo all the tragedy, and so Guster went smart and stupidly avoided the initial conflict between humans and monsters, creating a thriving civilisation.
There was never a barrier, there was never a war, no one died and no one suffered.
True, there was one tiny little problem.
Angel.
The Angel from the Prophecy, because the Prophecy still exists.
There is a prophecy. The Angel. The One Who Has Seen The Surface... They will return. And the underground will go empty.
And this prophecy is so old that even Gerson doesn't know where it came from, and it's probably a fundamental detail of the Andera multiverse, namely the arrival of the Angel.
Guster looked at Ander and realised that if some Chara or Asriel showed up in God form, it would ruin his "perfect scenario", so he came up with Delta Heroes, and basically this whole thing, just to **** with Angel.
THREE HEROES APPEARED TO BANISH THE ANGEL'S HEAVEN
And he called in a player to help him out a little bit, but someone interfered with his experiment, ****** up the vessel and shoved the player into Chris.
Guster didn't count on outside interference, especially not like this. Because Chris was never meant to be part of the experiment in the first place.
And then there's my theory that Ralzey is Guster's creation.
Ralzey knows a lot, and also knows details about Chris, because he's probably the red horns. But, they're gone.
And I think Guster stole them and threw them out into the dark world.
Ralzey said that the legend was whispered to him by time and space itself, and this version of the legend is much different from what other darkies know, and Ralzey also knows about the game buttons and even the save files. It's likely that Guster created Ralzey because Chris would be ******* pissed if some Lancer started telling him about the legend.
And Ralzey is this. sweet, kind, calm, Azzie-like, even knows you as a person, and totally tailored to Chris, just right for him.
Guster probably did it in a hurry and ****** it up, and the funny thing is, that plan is ******* ****** up too.)
As Ralzey began to question and think about what he really was, to think about what Ralzey was, because he realised that his good behaviour was a scotch-taped image, and clearly not the real him, i.e. he didn't know himself.
Guster's plan is ******* falling apart now, cos there's no Vessel, there's Chris, and the Prince of Darkness was created in haste to fit Chris.
I mean, two out of three characters have been changed, and it's not like Susie's the monster from the legend.
And Chris doesn't listen to commands, so he could ruin the whole thing by refusing to kill Angel.
Again, Guster created the Delta Heroes to kill Angel because he's in the way of a better ending, but his whole plan falls apart.)
Anyway, remember how I explained that Deltarun is a conflict between Guster and Angel?
Well, it's also a battle of ideologies.
1. You're not free, but you're loved, fed, watered and cared for. (You don't know that you're not free.)
2. You are free, you are free to be happy with your freedom, you get happiness on a spiritual level.
Okay, I'll explain it this way.
In Delta, as we remember, there are two opposing sides.
Guster and Angel.
Guster wants to free the world from Angel's tyranny and create a utopia, a better world for everyone.
But when I was sorting this out, I forgot something important.
Angel's victory has its perks, too.
Angel wants to release you from life and throw you into heaven, give you freedom from all this.
Independence from material possessions.
From earthly pleasures.
And gives happiness and freedom on a spiritual level.
Guster in turn, sinks for the familiar world, and comes out against Angel and his Paradise, trying to free the world from his rule and destiny of destroying the world he knows
Trying to make the happiest possible scenario for the humans.
I mean, both sides want to give freedom
But in different ways.
But each wants to give happiness.
In Guster's victory, freedom is lost, and every creature as well as the world becomes under his rule, but Guster wants and will make sure that his defendants are happy on earth. That everything goes well.
Unfreedom, but happiness in that unfreedom.
A battle of ideologies