system
Given the following post, respond as if you're commenting on Reddit:
human
[Lovecraft/Pokemon] What's the deal with Missingno?

I caught an odd... thing... the other day. 

Brought it up in the 'Dex, it just... blinked an odd red light a couple times, and hummed until it fried and sparked.

Meanwhile, the thing is, I've been getting boons... Strange boons. 

99 items, always in multiples of ninety nine have been washing up on the oceans. 

Been hearing strange whispers from the sea, of forbidden ancient caverns and creatures, of a language that life above has forgotten.

How does I learn it?
gpt
Don't. Take your boons, then release the Missingno and walk away. Some people who have had too many encounters with Missingno have reported permanent hallucinations. And there's rumors that it can get much worse.

As for what the cause is, it's generally believed to be a mistake made by Arceus. Something is wrong with reality, and whatever rules Arceus gave the universe are acting in a way they never intended.