That is an interesting idea, would love to have it implemented if given the chance

Here's a fun idea: since both active items that give Black and Soul hearts come with some sort of downside (one guarantees a Horseman encounter and the other turns the boss item into a devil deal), what if the Gravedigger's Handbook did what a piece of Mom's Shovel did, where you gain a bone heart, but you are cursed with the effects of The High Priestess? until you defeat a boss - with it coming with effectively no downside if used post boss encounter?

Aight, 8 charges it is

Should be 8 or 10 charge honestly. Bone hearts are pretty busted.

neat mod but i'd personally suggest buffing the charge on it to like 8 (5 charge is low for soul hearts letalone bone hearts) and possibly throwing it in some more pools (curse pool could fit but maybe some more diverse ones like the devil beggar pool)