Alright, let me first say sorry you have to read all of this but I hope you learn.
Your UI is completely inconsistent. Looking at your images I would’ve guessed the UI was designed by 3-4 different people. The font varies wildly between every menu, the design of some menus is similar while the design of others is very different. Shadows and textures are inconsistent and take away from the overall design, and the layout is different in situations where it could be similar.
Now I’ll go through your images and critique what I see:
Spacing and size of buttons on the left is inconsistent. The “gamepasses” text is right up against the edges and the button is smaller than the rest. Additionally, it doesn’t make sense why you wouldn’t have that included as a tab in the shop, same goes with currency. The “Information” title is not necessary and is in a completely different style than the rest of the menu, making it stand out but also look out of place. If you need to include a title for non-style reasons(I’ll get to this in a minute) then the only reason to have it is if people wouldn’t understand what they’re looking at, which should be fairly obvious in this case. A title kept for style reasons could be to fill empty space, help people to understand what they’re looking at, and to keep an overall theme if you use titles elsewhere. One way I like to think of using titles is if somebody that did not know the game were to come up behind me and look at what I’m looking at, would they understand what I’m looking at unless I explained it or there was a title?
The text does not stand out too well from the background and the color difference between buttons and the background is unnecessary until they hover over it, but really doesn’t take away from the style. The label that says “MLE off duty” does not belong above the tabs as it doesn’t belong with a list of menus. The tabs panel could be hidden off screen and when somebody moved their mouse to within a certain distance of the left side of the screen you could tween it in so that it’s not always in the way while they’re playing and not necessarily using it. You’re hiding screen real estate unnecessarily. The ready button doesn’t fit with anything else, same with the “all spells allowed”. I have no idea what they’re used for though. If the “all spells allowed” label is to let a user know if spells are allowed in a certain area, I would say put this as a small text label at the top-middle of the screen. Both the “ready” and “all spells allowed” text labels don’t match any sort of theme and are not too easy to read as there is no shadow behind them or TextStroke so if you were to look at the text over a background of even a remotely similar color, it would be impossible to see them.
The “guard power” button doesn’t make sense where it is, especially if the user could have more than 6 items in their backpack.I would suggest sticking it wherever you would move the “MLE” label to and change its style to match the rest of the ui as well. The galleons label is out of place where it is and unnecessary. If you want a user to be able to see their money at all times I would create an icon for the galleons and just put the number next to the icon in the corner where it is now. It’ll be smaller and seem less out of place. The font for the amount would have to be larger and bolder so that it’s easy to read and doesn’t seem out of place. This wouldn’t have to match any specific theme really. I would also suggest making a custom backpack and leaderboard as the default Roblox ones are useful for basic games but for a game that needs a nice and consistent ui feel they definitely don’t belong. Also I wouldn’t use a white or grey team color because it’s difficult to read the header in the leaderboard, just saying.
Not too many complaints here, but I would say make the previous and next buttons slightly smaller so that they don’t feel like they’re taking up the bottom of the pages. The table of requirements is completely out of place with a colored background and colored boxes, so I would design it in the same way as the rest of the book is. The triangle icon on page 3 is also out of place as it is really close to the top edge of the page and is not the same color as the text, not making it feel as if it is printed onto the page with the text. My other suggestion would be put the title page on the right page and leave the one to its left blank so that it feels like a proper book with the copyright page(the blank one) on the left and the title page on the right and then all the contents follow. The table of contents could also have this as the back of the title page is usually blank, but these are just nitpicky and you don’t need to really worry about them. I would also put the close button inside the book but not make it a giant red X but maybe just a small X in the corner being the same color as the text in the book.
Wow where do I start? It’s just a hodge-podge of different themes, inconsistencies and unnecessary stylizations. The ribbon that the tabs are on is unnecessary and causes the menu as a whole to feel unbalanced as the ribbon is sticking off the left side but nothing is sticking off of the right. The tabs text could be brown and slightly more bold so that it looks like it’s text written onto the canvas itself. I would sugges a brown/gold font here as it would look like ancient text on a canvas rather than the printed text on a book like the help ui. The title ribbon is shaded meanwhile the rest of the ui seems rather flat or has dropshadows rather than surface shadows. I would suggest making this a small piece of canvas that looks like it was attached(staples or pins would be cool) to the background canvas. This should also be centered as the whole menu feels off-centered because of this.
There should be a padding to the description, which could be written directly on the background and doesn’t necessarily need a box to be in. The description could also be larger so that it’s easier to read. The preview image in the top-right should have the same background it has in the menu itself because it just looks weird being on a white background. Again, it doesn’t necessarily need a background behind the image/title. The power, defense, etc. labels could be slightly more spaced out horizontally as everything to the right of the vertical bar seems rather cramped. Maybe put two spaces on either side of the bar or even replace it with a dash? This text should also be the brown that I suggested the tabs be in and should be slightly inset of the description(a few pixels further right than the description is) so that there is no easily noticeable straight line that everything is lined up with.
The equip, sell, can’t buy/buy and quit buttons should all be the same style and have consistent shading. The quit and can’t buy buttons are noticeably darker than the equip and sell buttons due to their shading. Also I would not overlay the can’t buy button on top of the buy button, I would just replace it. These buttons I would put closer together and maybe make slightly smaller. You really need a custom scrollbar, the white stands out like a sore thumb. The title font doesn’t have to be different than the rest of the fonts, it seems out of place the way it is.
Customize: (I’m assuming you accidentally swapped the images, but I’m describing what I see in the order you put it)
The title ribbon and tabs should be the same that I described above for the spells ui. Again, the spells title doesn’t need to be a different font and the font size is much larger than the spells ui title’s so it seems very odd when comparing the two. Change the CanvasSize in the “how to obtain” and “spell description” boxes so that you don’t see the scrollbar if the font isn’t long enough. Also you really need a custom scrollbar. Move the obtain box down towards the bottom and move the description down as well but space them out a little more, seems way too cramped the way it is. The title bubble should be moved down just to be inside of the canvas itself rather than stick out the top like it, doesn’t fit well like that. I don’t mind the design of it but add a bit of a drop shadow to the text (this could be done by making the TextStroke color 0,0,0 and setting it to .7 transparency). The design of the spells buttons is way too noticeable and there is no individuality in the buttons. There should be at least 2-3 designs and some of the rotated 180 so that it looks like there are 4-6 different designs. This would make the buttons look better as there wouldn’t be the same style to every single one. The text should also have a bit more padding and be slightly more bold if possible.
Way too cartoony in comparison to the other uis. I would use the same style you used for the Spells and Customize menus. I would also throw in the gamepasses here as well and change the name on the tabs panel to just be “Shop.” I am not going to spend the time critiquing it if I already told you to change it entirely.
The scroll looks nothing like the canvas you used above. I would suggest finding a piece of scroll that looks more like the canvas. The shadows are way too dark and it doesn’t fit the theme that the canvas menus defined. The icons don’t need that gradient behind them, that’s way too dark anyway. I would use the same colored background you used in the canvas menus. The label is too dark and hard to read, I would replace this with the small scroll you used for the item titles on the side of the canvas menus and making the font the same that you have there.The confirm button is just one of the default Roblox themes, baby what is you doing here. This should be replaced with one of the buttons used in the canvas menus. The arrow shoudl be a little bit lighter so that it doesn’t seem so dark and out of place when the rest of the ui is lighter. I would also make it smaller because it’s unnecessarily large right now and also overlaps with the confirm button which doesn’t look too great.
I would also change the colors of messages in the chat as they are too dark and hard to read.