Well this is the first online Co-op game I've seen in the jam, and I think the first I've played from a jam.  Which was a nice change of pace.  The gameplay was interesting and the mechanics left a lot of room for experimenting, mostly.  Though there were a few QoL things I would personally recommend adding.  A big one would be an easier way to see your friend across the river to have an idea what they're doing.  That or more distinct sounds for what they're doing, since currently they're pretty similar.  Though some finer points:

• Hit detection was a bit weird.  Specifically because it seems it's handled on a tile system, whereas the movement of both the player and the enemies is handled on a non tile based system.  Which lead to a lot of weirdness where I was unable to hit certain things when I wanted to.  I'm not sure how it's being handled game logic wise but a recommendation I could make would be to add a collider to the hammer when swung and whatever it collides with will be "hit".  Whether that's a chest, a skeleton or a rock.  It would take some extra tweaking to avoid it multi-breaking rocks I guess, but it would definitely make it easier for clearing what you want to.
• Adding the ability, somehow, to kill the skeletons would be very welcome.  Since currently you end up dealing with a horde you are essentially unable to counter.  Because the stun is so short, maybe lengthening it could help?  
• Making it easier to see your friend, as I said above, would be very helpful.  Because there was a decent amount of time where I would be waiting for my friend to see if he could get one of the chests with near no indication of what was going on.  Which lead to a lot of just sitting and waiting. So at least giving some vision on them could mix it up a bit.

I really want to try this but I have no one to play with :( but the art and the fact you made a multiplayer in such a small amount of time is freaking cool. Like how did you even test this did you have to build it every time? that would be a nightmare

Its amazing you can make a multi player game in a week!!! that art is amazing and it looks fun but sadly since its co-op i cant play it huhu.  but i will rate it anyway .

Nice game and Nice concept and idea.

For future improvement:

If players some how could see each other maybe it would have been better like a small camera looking over players and shows that to the other player like a minimap but centered on your partner rather than your self

This is the best game i have ever played but …

I did not play the game because  no one was online

but if the multiplayer system work (which is)

its the best game

it would be hard to make isn't it?

overall 5 stars!!!:)