Please note that the Gundams I pick will be mostly limited to what I've built, and my knowledge of the anime is VERY limited.

Mex
He is a dumbass but is sometimes smart and is pretty laidback
Ukulele
He exists as Patrick does to Spongebob, the sidekick who isn't intelligent either

Either a Leo or Leo space type for either of them

Hakai
Inkmatas
Peyton

Wait I just had a better idea

Spinatia commando type because of the horns

Probably remove the shoulders because it makes it a bit too bulky

And finally it'd be green and it'd have witchcraft weapons

For hakai, basically any version of the barbatos.

She may not wield a hammer but there is a version that has a sword

For inkmatas I think a spinatia with the witchcraft weapon set could work rather well

And it'd DEFINITELY be black and green

And for Peyton I think the nobell Gundam with different colors could work pretty well

(It has actual beam sabers I think but the ribbon is just an option. I haven't built this)

Rizu
Amber
Inky Pearl

For rizu...

Maybe a portanova marine type?

Ooooh

There's an expansion parts set that gives this a spear I think

For amber I think the lah Gundam works well.

For inky pearl I'm thinking basically any version of the core Gundam could work.

It's smol on its own but there's lots of different armor you can put on it to make it normal gundam sized

Just search "core Gundam" and see which one you like

Autumn: She is a normal human that has a gun
Potato

Demi trainer and chuchu's Demi trainer

Scribble
Diana (no image yet, srry!)
Rose
Switch
Rampage

Uhh

I don't know any of these characters well :(

Sorry

Oh

Scrib is the type of guy to draw anything he sees
Rose is silly, but can basically be the inkling equivalant of LTG
Switch is... Switch
Rampage is basically LTG but an octo

oh yeah and mayu exists, so-

Who is ltg?

Low tier god

I don't know much about ltg other than the keep yourself safe template

And diana is basically the vessel of Artemis

Could you give a description of each of them?

Matt
Eren
Violet
Ares

I don't know any of them :(

Okay :(

Maybe just give a description of them?

matt: Litterally just a guy gifted with god abilites. nonchalant at best but will punch stuff if needed
Eren: loose cannon. Falls asleep alot
Violet: Kind but will kill you if you insult her or her friends
Ares: The god of war. need I say more?

Since Matt is basically just a normal dude I feel like the RX: 78-2 Gundam fits well.

Relatively basic among Mecha designs, but still cool

The rest will take a bit more thinking

alr

Hmm...

Maybe the z'gok could work well for Violet?

Something about the claws just... works.

Yeah I guess

As for what a couple of my characters would pilot, here they are.

Collector would pilot the shin burning Gundam, but with some minor changes.

The armor would have a similar color scheme to his armor, the Japanese symbols in the shoulders would be changed to look like the crystal of creation, and the flames would be changed to blue

For Astra... This took a bit of thinking.

But eventually I came up with this, the Gundam aerial.

Just like collector, the colors would be changed to match her colors, and the dark orange segments on the chest, legs, and head would be changed to dark blue

I haven't really thought of anything for my other characters but if you're curious I can try to think of something

Yoooo I got that one :D

Saike
Milo
Lay

Both Milo and Lay would pilot different colored versions of the nyaia Gundam

I'm not sure if this is real or fan-made but I think it fits well

It's a modified version of the Gaia Gundam which transforms into a wolf if I remember right

For saike, the Gundam astray red frame inversion

The original has white armor and the red is a bit less dark

Perfect for both

Rift, I'm pretty sure she's the only one smart enough for that