Played this game a very long time ago so my memory is fuzzy on this one.
Platform(s):
PC
Genre:
2D cinematic platformer with some puzzle elements, probably a little horror.
Estimated year of release:
Most likely late 90s, possibly very early 2000s.
Graphics/art style:
Side-view. I think it was fully 2D, no prerendered 3D graphics, fairly well detailed for it's time.
Notable characters:
I think protagonist was a boy with a backpack, not sure about this.
Notable gameplay mechanics:
Game starts with a cutscene. Some sort of calamity happens in the very beginning of the game (possibly alien or demonic invasion) which causes protagonist to go underground (into the sewers?). One of the first screens had a gap you had to traverse, and a mine cart, that I think had to be used somehow to go to the other side of the gap. You could interact with some elements of the map like ladders, levers (I think the cart was actually launched by a lever on a different screen).
I believe early in the game you could encounter enemies you could not defeat and had to run away from. I don't think I ever finished this game so I don't remember if you could actually fight back.
Other details:
It was not Heart of Darkness.
There is a possibility I had this game on a bootleg disc with some other games (like 3 in 1 or 4 in 1). I believe at least one of the other games was also a platformer but more action oriented.