This is a fantastic mechanic and is really interesting and fun to play.  However, the learning curve is way too high -- you're assuming the player will be able to figure out the mechanic immediately, and that's not a great assumption, especially with instakill spikes there, especially when those instakill spikes' hit detection extends to their side so players feel like they get an unfair death.

Actually, honestly, remove the spikes, at least from the first level, and this is great.  Not a fan of lives in general either though, but that might be my own preference.  Oh, and actually, when deselecting blocks, sometimes it works and sometimes it doesn't, and it's hard to figure out why this is, and it can be very frustrating if you thought of a clever solution to a predictament you're in, and it doesn't work because you arbitrarily can't deselect a piece.

But what I really like about this mechanic is how divergent the gameplay becomes.  Players can have a completely different experience of the same level and can form completely different shapes and solve different problems within a fairly simple space, and that's a really amazing and impressive thing. 

For example, I wound up in a large inverted L shape and decided to grab a tile in the floor to my mistake, falling to grab the floor above me that I was just standing on.  I was too large to jump up, so I thought initially that I made a mistake an had to restart.  But then I realized I could jettison the bottom blocks below me to make the bottom part of that inverted L smaller so I was then able to clear the jump and make it up to the floor I had just fallen through.  It's an interesting puzzle that happened simply because of my own mistake (so most other players wouldn't even experience this), but I was able to get out of the situation because of natural and interesting consequences of the mechanics.

Also you should be able to select multiple tiles at once, pressing Q then E is kind of annoying.

Anyway great mechanic and stuff.

Edit: So after reading the credits I went and played some of Un Blend, and yeah, the only real differences are the level design and jump height.  Magnet Join ends up being more chaotic as a result; it feels less designed and more divergent in comparison, which is bad for learning the mechanic initially but great for player choice and replay value.

Such an interesting take on the theme! Super challenging! Great work :)

Challenging game! I included it in my GMTK compilation video series, if you’d like to take a look. :)

Great game! I loved! :D the idea is amazing and very well implemented, it really got me thinking

I love how it allows for so many different ways to move and to solve stuff

Really cool concept to use the block level as a partner, I like that idea a lot. The music is fun and great SFX, good job !

Really liked the idea, and the presentation is awesome

Nice idea im dum tho

Apparently, like everyone else, the first red spikes spelled death for my attempt :(

Really cool and fun but i was too dumb to get past the spikes. the controls too a little bit to get used to but i loved feeling like i was building the level.. with the level!

Really interesting game.  Took me a while to get past the first level but it was really fun. Great job and make sure to check out our game too https://crispystudios.itch.io/net-catcher

I might be an idiot, but I couldn't get passed the first level. Still, a cool idea! Has legs for sure.

Very unique gameplay, I see lots of potential in this mechanic! Thanks for creating this!

Some thoughts on how to make the better: add a longer music loop. :) Build a less steep learning curve, where players have to create small constructions first, instead of really big/high ones practically right from the start. Be more forgiving – don't destroy big creations that took a long time when stepping on a single spike.

super cool! :D

It was good but I couldn't figure out the part where there is the three red spikes on level 1.