Recently I've been enjoying the excellent Dead Cells and I found it interesting to see that the game puts all of its vital HUD information (health bar, item keys, map, etc) at the bottom of the screen. Pic for reference: http://imgur.com/a/0pLmt

That's not new to videogames by any means, we usually see HUDs at the bottom in FPSs, where it's closer to the gun you're holding, MMORPGs, MOBAs, and in a few other genres. But the thing is, that's not usually the case for games whithin this particular genre (read here "metroidvania", platformers, or pretty much sidescrollers in general).

They usually place this kind of information at the top of the screen, often closer to the left corner. I'd assume that's in order to prevent it from distracting the player from the action itself, which tends to happen towards the bottom in these kinds of games (think traps and platforming). But when you consider Metroid or SoTN-style Castlevania or any other generally similar games, much like in Dead Cells, there's a lot going on at the top as well: enemies, pathways, details leading to secrets, etc. Is there any other reasoning to why the HUD tends to be at the top? Is it just an old convention that games didn't really want to break? Is it ok to change it? Feel free to give any thoughts on that.

It works well on Dead Cells. The HUD is usually below the ground level, which means it doesn't block the action all that often, and it leaves space for us to see what's going on with higher platforms or flying enemies. I think it's aesthetically pleasing, too. Do you remember any other sicrescrollers that put the HUD at the bottom of the screen? I'd love to see some other references as well.