Ask Softmare!

In SWAPsoft, things would happen the same until the accident, which while Nightmare goes rouge, Dream calms down and gathers as much as positive energy as he could to challenge the negativity levels that were going through the roof. He can only subdue the negativity once he takes a bite out of his own positive apple soul, which hurt like hell, but worked and Nightmare became stone instead.

Unfortunately, Dream was too late to think of it so mostly everyone was already dead, leaving him alone to look around the empty village and soon the forest nearby. Due to the soul bite he was weak, so weak he didn't notice a deep dark valley that he fell into. The way down was rough, pointy rocks scraped against Dream's bones harshly (the fall also cracked a few of his bones), and as any child, he was afraid of the dark.

The steep passage to the top was impossible to climb alone, even if he tried, he'd fall back into the valley narrow space he was limited to. He only managed to get out once Ink appeared, taking him to the surface once again before he rushed to help his brother (who just like original Softmare has passive Nightmare's memories) and both tried making up for the confusion. Nightmare apologized, helped Dream to care for his bruises and moved with him to the Omega Timeline.

Here, Nightmare seems more lively and aware, with an introverted personality that rejects loud people of course, but he still isn't bad... He satiates his hunger by offering "free therapy sessions" to Omega Timeline residents in which he doesn't really listen to the rants, but eats the negativity so people feel better anyway. His eye is normal sized, regulating itself just fine in the dark or in too much light.

Dream is the more quiet extroverted who would like to start conversations but finds it too hard and just stares. His eyes were damaged by the darkness of the valley, so despite having both his eyes, he sees really bad because they don't adapt to different light levels. Dream is terrified of the dark and closed spaces, he is also not very sensitive to physical pain since he felt it too much in the valley.

Being smaller still, Nightmare tries to be Dream's much needed older brother figure, treating him to sweets, finding easy people for him to talk and practicing interactions with him.

Dream sees Nightmare as no different from Passive, to him they are the absolute same person he loved since the beginning of his life, needless to say that he cares A LOT for his brother despite being the one needing help here.

Now, how did he get into the OG universe? OG Dream lost a battle and they needed a substitute, the victim? Softtale Dream! When he got there Ink was so pushy he creep the guy off, Swap was his first friend and Outer was an okay guy to hang out with (Outer was recruited briefly to cover for OG's disappearance, soon after Dream appeared he was dispensed)

And yes, OG Nightmare is CRUEL to him. But fortunately Dream's aura is a bit more neutral than OG's... Making it easier to endure the negative energy from OG Nightmare attacks, he doesn't even mind the burns the goop gives him since his pain sensitivity is really low.