I can hear the screaming now.
When I found that letter, I didn't listen at first. Well, perhaps it would be more accurate to say I didn't listen at second. I must have done as you asked the first time around, seeing as I didn't remember anything about you. But after finding your warning again, I thought it was just a joke past me was playing on future me. I shared it with Butter Breeze, one of Fluttershy's descendants, and we talked about it for a while before dismissing it as a prank.
I rarely spent much time in one place anymore. So many interesting things happening across all of Equestria. Oh, Twilight, you would have loved to see how far society had advanced. At any rate, it was a month before I returned to visit our friend's descendants, only to find that half the town was missing. And of those that remained, the vast majority complained about a constant noise, like screaming, keeping them up at all hours of the night.
Even then, I didn't recognize the threat for what it was. I thought it was all part of a mean-spirited prank I was pulling on myself. Yes, I've pranked my future selves before. And my past selves. And my present selves. The point is, I thought this was another self prank, and I had fully intended to find the past me to give me a piece of our mind, about a paw full to be precise, about the whole thing going too far. However, none of the past mes, not even the mes from before my reformation, knew anything about what was going on.
(As per the self prank guidelines, and yes, we do have those, we erased our memories of our confrontations afterwards. In retrospect, that probably saved the space-time continuum and led to my current predicament, but we just wanted to avoid giving ourselves spoilers.)
By the time I got back from my confrontations with myselves, Ponyville was completely empty. Even worse, the effect was spreading throughout most of Equestria at this point. By then, I knew this was far more serious than a prank, but it was too late for me to stop it. Too many creatures affected, too many memories of beings that no longer existed to erase. I tried my best, but when the princesses stopped existing, all Tartarus broke loose. Somecreatures blamed me for what was happening, while others thought I no longer existed, and did their best to ignore me.
I likely owe my survival so far due to not following the pattern-seeking mentality all the others did. This seemed to serve as a camouflage against the non-entities, allowing me to avoid their notice while easier pickings were all around Equestria. But there are so few creatures that still exist, and the nonexistent are seeking me out now.
While I may not seek out patterns, I'm still not able to grasp the concept of nonexistence. My mind still seeks to fill it with something I can comprehend, and the non-entities are still affected by this. They're learning to search for me, how to trick me into seeing patterns through which they can manifest. Soon, even with all the power I possess, they will overcome me with their screaming. But I still have time for one more act of defiance, one act of spite before I'm brought down.
I'll call them Pattern Screamers.