I got to the part where there was an NPC but they are on a platform surrounded by spikes so I couldn't figure out what to do. Plus getting there is so hard I only managed about 3 attempts to get past it.
The inclusion of checkpoints would have been handy since the game is so unforgiving in difficulty :)
Colliding with an NPC triggers some dialogue, then you just backtrack to the door in the center (your progress is displayed there if you look closely). There is something of a checkpoint system but it's not quite as blatant as it might seem. Something super involved just didn't seem necessary for something so small.
Apologies for my vagueness, but I don't like just saying the features flat-out, especially when my account activity is displayed for everyone on the platform. I think it ruins the fun.
