How to make armour that makes you bigger or smaller

With the tools inside MCreator, no, there's not. That takes some advanced coding to be able to pull off

@#1.1 First way. You have to go into coding. To do this you need to add a code line in the armore peaces, when worn, you need to mess with a player model Gl Scale, but the sad thing is i dount know such a code line soo you have to figure out your self.

Second way i know, you can use custom mobs. No need for equipment, just make a mob, with no ai. There was a custom mountable mob tutorial in user custom codes, but https://mcreator.pylo.co/custom-codes the link no longer works coz you can see, page no longer exist. You can still find the code line but you have to search thet by your self, i can only give you this inf that it was used by dude called KillerUnicorns in youtube video, mcreator tutorials. Soo your mob is made mountable, the next tricky part that i havent done is to go again into coding, or figure out another way, you need to make your self invisible when mounting a mob soo it looks like you are the mob. And if you figure out a way how to do it, you can add there more diferent potions eff, like for Hulk streingth, speed and jump boost.

I hope that i have messed up a bit your mind  :D and i hope now you know that the thing you want to do is pretty hard or imposible for modders like MCreator users. And offcourse gl with your mods dude

@#1.1.1 That's actually a really interesting and creative way of pulling this off. Theoretically, you could totally just mess with the scale of the player, which I'm sure would be a much cleaner way of doing it, but I don't know how to do that and neither do most people. That's why we use MCreator instead of straight up Java! :)

Nice idea though, I would never have thought of that mob mounting technique

Umm, i have an idea, there is a Gl scale code line in techne mobs, maybe something from there