Only characters I know are included; those I have little information about were left out. The list is roughly from least to most dangerous, from right to left.
Aldebaran's authority is simply terrifying.
In an alternate route of the game Re:Zero Lost in Memories, Subaru manages to convince Priscilla to join the fight against Petelgeuse, which also involves Aldebaran.
The battle progresses as in other routes, but when they face the Archbishop of Sloth, it is Aldebaran who first enters the fray, following his Mistress's orders. Just before going into action, he activates his checkpoint, preparing to die again and again.
Despite not being able to see Petelgeuse's invisible hands, Aldebaran relies on his only method:
Trial and error. It is through countless attempts, blindly dodging, that he finally reaches a point where he manages to land a single, precise, and fatal blow. At that moment, Petelgeuse attempts to transfer into Subaru's body, but Priscilla intervenes and finishes him off, reducing him to ashes with her fire magic.
Aldebaran won without any scratches.
It is also due to the nature of the ability, Subaru cannot control his checkpoint, so he has to think further ahead; conversely, Al decides when to activate his, which facilitates trial and error.
Al's ability is better suited for bosses, while Subaru's is for dungeons.
Do you think Aldebaran could have defeated the whole lot of them all by himself, without any allies?
They needed Felix to prevent Aldabaran from committing suicide, and Reinhard to immobilize him. Reinhard had the ability to choose where he would revive, which caused immense frustration because he had already dealt with his exasperating immunities and it took a long time to find a weakness. And although they hoped no one would break Ol Shamak, it turned out that Reinhard's sword reacted and could do so.
Reinhard literally had to split Aldebaran to extract Subaru and Beatrice; he could not have saved them without the help of Felix, who healed Aldebaran.
So many things Aldabaran did, like not killing people, only made matters worse.
With Rom, they discovered his authority, and with help, they realized that Aldabaran needed to die.
He had to lose because he was the antagonist, but his desperation was palpable. The smartest and strongest were constantly facing him.
Subaru and Aldebaran's abilities are similar but have their differences. While Subaru's Return by Death ability updates automatically and works anywhere, giving him several days to counter problems, or only a short time if the problem doesn't require it, Aldebaran creates a domain where his ability functions. Therefore, he has to manually update his save points. It's unknown how far back he can go, but he seems to prefer doing so in short periods. This ability to manually update gives him a tactical advantage in combat, allowing him to constantly refresh his save points. Since it was only mentioned that Al must die in the domain for his ability to work, he may be able to go back quite a long time if he doesn't leave his domain.