Part of what makes roguelikes both fun and frustrating is the knowledge that something is important, even if you don’t know why. RAD does this with the Mender Altar by putting it on the map and making it a seemingly important element, except it isn’t clear what or how you use it.
Surprisingly, there is no guaranteed way to activate the Mender Altar. Depending on what and if you kill an enemy close enough to it you’ll receive something, it just doesn’t always seem to trigger. This could be because each version has a specific number of sacrifices required or possibly not being close enough to activate it or maybe even something else.
Whatever the secret might be, all you can do is kite enemies to the spooky altar and hope it activates upon killing a foe. For doing this you can earn one of three trophy/achievements, plus a prize. One is a health item, another is cash and the final is in the form of a punishment. There doesn’t seem to be a way to determine which you’ll get, possibly enemy tier or just dumb luck, though trophy percents seem to indicate a drink is most common, followed by disapproval and payout being fairly close to one another at 2.5 and 2.2 percent respectively.
However, given life and cash is always a bonus, I strongly suggest trying to make use of it whenever possible. Worst case you eventually get a trophy/achievement and best case your run in a little easier. Plus, maybe it will unlock some cool items in the future, as games like this have tons of secrets one person can’t possibly figure out. Be it a new character, weapon or maybe even a different item, you really have nothing to lose besides health. Plus, even if that occurs, you can always use this trick and press your luck.