Yeah, the PIDRNG determines Natures/Encounter Slot/Shininess. The main window will tell you what frame has what if you paste the seed into it, and don't forget to click "Calculate Starting PID frame" when you do. From there, use Chatots with a custom Chatter or walk around in the cave with a Repel (Chatot will advance 1 frame for each summary, walking or turning in the cave advances 2 frames each turn/step).
Thanks for the help! Also, i finally found my SID, which means i can RNG shinies now.
EDIT: So many problems with RNG, but i know that the outcome will be well worth it!
I tried to RNG a shiny terrakion (i didn't save after catching the non-shiny flawless terrakion before) and i did everything correctly, but it didn't work (and i used the calculate initial PIDRNG frame on the main window to find out my ISF).
I did a test to see if my theory was correct (that something is wrong with keypresses) and searched for a seed for a shiny jolly terrakion with completely random IVs, but with no keypresses.
I calculated my chatters, hit the seed, caught it and checked it's IVs.
The IVs where exactly like the ones i got from my seed, and it was shiny!
The terrakion i caught before (non-shiny flawless) also had a seed with no keypresses.
So now i am asking, does it matter if i press the keys too early?
for example: My keypresses are select + X + A.
When i start my game (after changing time/date), i hold the select and the X buttons.
When the time comes, i hold A and start the game (pressing A starts the game).
I keep holding them until pokemon company/nintendo comes.