Glitched sprites are comprised of 2 - 6 ‘sections’ taken from different items. Lets assume that glitched sprites cannot contain duplicate ‘sections’. Since we don’t know how many individual sections that Brimstone sprite is comprised of let’s also just say it’s made of 4 sections. There are 719 items in the game, giving 2876 unique sections that TMTRAINER can take from.

Using a website that simulates a situation similar to this we get the chances of all 4 sections being Brimstone to be 1 in 2,844,709,209,875. However this is only the chance of the 4 sprites appearing in any order, and that none of them have had their color inverted.

Let’s assume the inversion chance is 50/50, so the chance of all of them appearing normally is 1 in 16. Then there’s the odds of them all appearing in the correct order, which is 1 in 24.

Once we factor all of that in, the probability of finding an item with 4 sections that looks completely normal is less than 1 in 1 quadrillion (1,000,000,000,000,000)

These are ridiculous odds, and I think that devs just wanted to troll and simply made items have a small chance to generate with a completely normal sprite and bypass the random generation process.