Hello, thank you for both your answers!
I did a few more tries on Queen Mimic, but didn't work.
I tried elsewhere, I tried to steal the Rare Item from the mark "Rocktoise" with the cure system and it did work well. So, yes, it won't be possible to steal everywhere, according the capacity, or not, to prepare the RNG before.
So I thank you all again for showing us the way.
I already did the classic version at 100%, I love this game and I'm going to use that RNG manip to have some more fun
