or can i even make a specific color deadly?
this might sound dumb.. but as i sad. i have almost no experience.
The code really isn't set up to easily make changes like that, but it's possible.
Hazards are stored at line 590, "if tils(px,py,px+7,py+7, [tile index] ) then die() end" will turn [tile index] into a hazard.
The heart is not actually an animated tile but a sprite drawn at the level's end. TIC-80 does have support for animated tiles through writing special "remap" functions, but this game does not use one.
Making a specific colour deadly is possible but much more difficult than making a tile deadly, I'd stick with the method I described above.
If you're this interested in modding Celesteditor have you considered trying to make your own game? Making something like this isn't as complicated as it might seem using a tutorial like this one, and it would mean that you aren't restricted to building off of someone else's game.
well.. i can try..