Hey Vasilis, thank you for your feedback!
There is indeed an ending- every "stage" has different mechanics and setup, and the boat fight is considered level 1 (it goes: lighthouse w/ the grandma is level 0, boat fight is level 1, platforming is level 2, ascension is level 3, final witch fight is level 4). You should be fighting waves of enemies, about 5; if you keep fighting the ranged attackers on the boat, it might mean that you died and respawned at the checkpoint.
I believe some of the comments you made about the ranged attackers coming closer are forced to happen in later levels due to level design, but definitely a good comment, as is the damage feedback! Game juice is definitely something that would be fun to experiment with- it might also be a better indicator of death as well. The progress indicator would also be a fun ui element to explore as well. Thank you for playing and enjoying MonMon! c: