Replacing power-up tiers with HP for player

[fawfulthegreat64]

I'm trying to make something themed around Super Paper Mario, and I don't really think the traditional Mario power-up system works that well for this. I'm wondering what I need to do to make it a health system, where a mushroom/heart heals health and getting hit decreases it without a visual change in form.

I'm kind of new to this, I've been able to transform one of the Goombas into a Squiglet that has left and right facing sprites (which simple a change as that is, it threw me for a huge loop and I'm surprised yet relieved I was able to get it working without asking for help on that one). Otherwise, all I've done is some graphics changes to the tiles and Mario (though Mario still has a glitched death animation that shows both frames on top of each other and I don't know how to fix that, I'm using the SMW Mario)

I've seen some threads that seem to be about health for NPCs, which I'll check out, but I wanted to get the player's HP sorted out first which I didn't see anything on.