[RedKey]

Alright, solved it.

Spoiler for riddle solution:

I feel bad that I couldn't think of anything from those strings of numbers until I saw the arranged pic from Mr.Q. I really thought some kind of cypher was involved Yeah, I'm not so good at riddles.
I thought the numbers had something to do with bytes, so i divided them in groups of eight like this

12000034
52000036
72000038
9200003A
B200003C
72000038
52000036
12000034

...and got stuck. Seeing the chessboard this morning made everything click. Once you get there, finding what mate is being shown is pretty straightforward.
Many thanks to everyone, I don't think I would have been able to move further than the message and fully appreciate the riddle without you!

A well thought riddle indeed, Jan-Poo. Bravo!
(...a trolling elephant? )