I reset for 10 hours so my Thundurus in Legends Arceus was Impish natured and had the "Mischievous" characteristic... I couldnt even get one with Mischievous so I settled for "Likes to thrash about"
>>59354770Characteristics are determined by which of a Pokémon's IVs are the highest, and what that highest value is. >see:https://bulbapedia.bulbagarden.net/wiki/CharacteristicStarting in Gen 6, games guarantee a minimum of three perfect IVs (with a value of 31) for all legendary Pokémon. This restricts the variety of characteristics that you can get on that Thundurus. It can only get characteristics from the second row of the chart in the link above.Luckily for you, that does include "Mischievous," so I think that you could technically still do it in P:LA if you keep trying (assuming that the modulo calculation doesn't stop you. I'm not going to do the math on that to try to figure out whether it's still possible or not.) If you really want to get a Thundurus with the "Mischievous" characteristic (and if you have a DS and an old copy of a Gen 5 game), I would suggest that you get into RNG manipulation and just do it that way.Gen 5 is very easy to RNG manipulate in. All you need is a tiny bit of patience for the randomness.
>>59354786Thank you for the explanation anon, I knew it related to IVs but I didn't know it had to do with the personality valueMischievous is possible because I got Impish/Mischievous Tornadus without even trying, and I wanted Thundurus to match but this is close enough