You have a bunch of icons on the right side of the menu screen. I can guess at some of them, but am not certain. It would be nice if you added hover text/tooltips to say what each does, and if any leave the game/open a web page. With your very heavy marketing push everywhere I'm not comfortable clicking on most of them, out of concern for if they might open external links & where it might take me.
When I got to the NPC that brought up the "Blocks" shop screen the text says "Please... I only need a single block.", implying they want a block from you, but it looks like the currency is keys that you can use to buy blocks.
The next one over looks like it is selling your real world pack, with 3 spots showing the same thing, and feels out of place. I just started playing and one of the first things I'm interacting with is trying to sell things for real money makes this feel like a cash-grab freemium game. Your web-page is already so heavy with marketing, that it makes this feel even worse. If not for playing as part of our jam, I'd stop right here. Even if I came across this in another jam, I'd be done. It is even worse that you put this in next to the in-game shops that you will likely need to visit many times.
As I've played more I see that all of these shop NPCs are scattered around the game. Your push for selling a real world pack in-game is excessive. If you really feel the need to include it in the game, put it off to the side of the main area, once, not scattered along with the others. If someone wants to buy the pack, they can go back to the main area. It really does not need to be everywhere, and every time I see that NPC pop up again it makes me think less of the game. Really, it doesn't even belong in the game world. Having a clearly marked spot on the main menu should be the only place. You are detracting from the game and pushing people away. Has this heavy handed approach really been making you money? Sure, big game studios can be heavy handed, but they have the user base numbers to get those people who will randomly spend money. For a smaller studio or dev, you are more likely to push people away with so much pushing to sell real world content so early and throughout your game.
I had issues with the shops. After collecting 500 coins, and putting 1 gold block in place, I tried to buy another. The screen shook and the was a sound, but I did not have a new block and no money was lost. When I reopened the shop it showed a grey block. Clicking that had the same results, except switching back to the gold block. I tried the key based shop and had similar. I guessed that maybe it didn't use the mouse, and started pressing keys on the keyboard. I eventually tried tabbing through to see if something would be selected, and that resulted in eventually tabbing out of the game and the screen shifting up so it was unplayable. I had to refresh the page to play further. After the restart I was able to make a purchase, though it was on the grey block at that point so I was not able to afford the gold one. I then tried the key based shop. I had 8 keys. I bought 2 grey blocks, without the # of keys going down. I was able to get a total of 4 keys this way, with it sometimes giving me a key, and sometimes closing without, until it got to always closing without. My # of keys never went down.
Space is listed as interact in the controls, but it also seems to cycle through the icon at the top right for Block type to place. At this point I am not certain if the interaction is only with people, or there might be other things to interact with, so it would be nice if the interact button was dedicated and not also tied to other things.
I went back to the first person to double-check the controls, and now they are saying the same thing as most of the other people. Since you have the tutorial controls message tied to an NPC, it would be nice if that spot always had it, rather than switching to something generic. If you had updated info, that could work for changing, but changing to generic doesn't make sense.
It would also be nice if all other controls were listed somewhere in-game. I'd add a few NPCs in the starting area with the controls and any other tutorial info for the player. They should not change their text, so players can refer back when needed. I don't recall seeing anywhere even list how to place a block after buying.
I completed 19.52% of the game and returned 1 gold block, with a 2nd being thwarted by the shop bug. The puzzles are decent. Being able to buy blocks helps to deal with any that a player can't figure out or makes a mistake they can't recover from. The flipping works well, and the indicators of what is in the other world is good. I think the merchants are more common than needed, at least in area 1. Purchasing blocks was not needed there, and it is easy enough to backtrack a short distance if you need them. The addition of NPCs does add to the world, I'd just add them more in moderation. Instead of adding a bunch saying the same thing now, add them as you have new text for them, and try to give a bit more individuality to them. There were some good updates here, but you still have such a strong push for trying to sell things everywhere that you are majorly lessening the feel of the game.