Alright, here's my feedback!
I really like how the jump feels! The gravity is well handled and it doesn't feel floaty nor bricky, which is a frequent issue in beginner platformers. And although I think the jump could be improved with a coyote time, I also get that it's a difficult mechanic to implement especially in such a short timeframe and double especially as a first game jam game, also a risk cost if you don't know how to implement it which usually spawns in some glitches, so I'm glad you spent the time elsewhere.
The wall jumping needs some getting used to and is more difficult in the beginning tutorial areas than in the actual stealth sections of the game, mainly due to a level design issue I'll get to. But for now I'd like to say that it doesn't do the game a service to have the tutorial be a platforming difficulty spike when the core gameplay loop is centered around stealth. It could make some players that dislike difficult platformers feel frustrated and miss out on the biggest strength of the game, which is a shame, because the stealth is super fun!
The game has no AZERTY keyboard support which is a shame. I know to change my keyboard language settings to fix this issue, but not every AZERTY player knows this trick, and it doesn't even work on every game engine. I don't know how input handling works in GameMaker, nor do I know if changing keybinds is easy to implement, so I can't really blame you for this either, especially since this fix would've required more time which you had in short supply, and if this is your first game or first time runnning into this issue I can understand the oversight.
Early on in the platforming level, there is a rather tricky wall jump (with a staircase below it) made unintuitive by the character bonking their head on the platform above when jumping off. Since there is no coyote time, it's even more difficult to time that jump right, and I feel like this could've been fixed by simply adding one more tile to the staircase and moving the wall the player must jump on a bit further back– or even not at all since the player is still getting used to the mechanics there.
In this same area, the player must jump on a very small platform and slides off it, it would've been more accessible to newer players if that platform was wider, or if the intent was to force a wall jump in this section then the platform should go even higher to prevent the player from ever reaching the top with a single jump. If they don't jump too early and bonk their head on the block above, the player often instead slides down the staircase when winding up to make that jump, which adds to the frustration in this specific area and makes it a bit unfair to newer players.
In your future games, I'd recommend you do more external playtesting, since you would've been able to catch those issues much earlier on and fix the easy ones or accommodate the level design to go around those issues. I don't know if that's what's went on, but it reminds me of times I playtested my own projects so much that it became trivially easy for me, and when confronted to external playtesting I was hesitant to make it easier because I worried it would become boring or too easy. Ironically, it is much harder to make an easy level than it is to make a difficult one, especially if it's a tutorial level or a first level which needs to teach or reinforce mechanics. But I still find your Level Design to be encouraging! Keep it up, and do more playtesting to catch any issues early on! In my experience, playtesting has also helped me be more okay with failing, and changing mechanics that don't work even if I'm attached to them, it taught me to "kill my darlings" as they say, or patch bugs which I knew were there but got used to working around, this can only improve your games!
The assassination mechanic feels really good! The sound effect is really well chosen and the feedbacks are great! You can easily understand how your hitbox looks like thanks to the smear effect. I also really like the shuriken and think it's a great idea to limit its use when on full health, incentivising players to take risks by preventing them from spamming an easy solution is really smart, and keeps the intended stealth user experience intact! Great work on the stealth sections!