What worked:
It's a very creative idea. I like the part where you have to carry the other after falling. The different characters revealing secrets in each room (keys, platforms) is really cool. I didn't get very far due to time, but it seems like there are some great puzzles ahead.
What didn't:
I would love some feedback on how far the tether is. Something visual or sound based to let me know I'm reaching the limit before I get there.
Swapping can feel kind of slow at times.
The character collision boxes feel a bit too big, making it easy to run into spikes.
Bugs:
After turning upside down, I couldn't find the key so decided to backtrack. This was a bad idea as I ended up phasing through a wall and getting stuck in the first bridge area.
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Great job!