just make shadows of the adopts - a pretty background - put a flat price for a roll, offer 1 re-roll free - additional re-rolls pay a little extra

use a random number picker to choose what they get

if you need more help you can DM me ^^

Wow!!! Gacha has so many species, it's unusual! In my country in gacha, you can choose any of the characters, you just don't know what exactly is waiting for you there, only an approximate box/description/piece of the character, so I made this auction! This is very cool, thank you very much for the explanation!!! However, thank you more, this is incredibly useful information for me, I will try to make such a gacha as you described! You are incrediblе (ಥ﹏ಥ)

there is lots of different ways to do gatcha! that's just 1 of many ways - and is a fun way to sell designs ^^