Trying to make a custom dweller, can sum1 help?

Hello! Im currently trying to understand (and failing) MCreator, exactly im trying to do a custom dweller/monster/horror mod, wich i have rn the model (VERY bad, but ill make it better), and some ideas for it:

First one: i want it to have a passive and an attacking mode, like, sometimes it will be passive, and dissappear after two minutes, or if the player gets close enough (like 5 blocks distance, and will give the player some effect like he hit his head or sum.)

Second: make custom AI, if you know the "mimicer" mod, you know it spawns in places that the player could go to, and then after the player sees it, it makes a custom scene/talk (wich i wanna do too).

Third: the creature can make infected mobs/players, it can be hostile to mobs and thing, and replace them (like a doppelganger).

Im makin exactly an alternate from MC (Mandela Catalogue) so it'll be cool if some of yall can help me (i have NO experience using MCreator, im very sorry :c).

Thanks!