>>13627293alright, this going to get a bit convoluted so keep up with me
the gacha system in genshin has a pity system that depends on how many rolls you did on a type of banner ( Character and Weapons banners are considered different for this system ), once every 90 pulls on a character banner you have 50/50 chance of getting the adverstised unit or getting one of the five 5 star characters from the permanent gacha ( Mona, Diluc, Qiqi, Keqing, Jean) and on the 180th pull of a type of banner you'll get the advertised unit in the banner should you missed on it on the previous 50/50 check.
so if you want the best chance to get Mona you should make sure your 90th pull is on the permanent banner for a 20% chance of getting her
