Thanks for playing the game, and for the kind words, and feedback!
I hate to be the bearer of bad news, but you don't have to sacrifice anything to be able to fight the 4 bosses.
"... and the alter become a place where the player brings some energy orb thingy that they get for beating the bosses to open up the next boss room... " - That's basically how it works. You either need to sacrifice 4 health, or 4 boss souls to open the path to the final boss.
I do give you that it's not "badly" explained, it's not explained at all. A bit of exploratory design if you will.
The controller support for menu's is on point, no excuses. I just didn't want to deal with it.
Tergesa looks wonderful, I'll be sure to give it a go in the upcoming days!