The drop rates are way too low on the boss relics. I shouldn't be able to beat a boss 50k times and not have picked it up. I know they're only one time drops, so they should be rarer, but it is kind of ridiculous.
I didn't even realize until this comment they could drop boss relics because it says in their loot table that they only drop money. I thought the relics would be from some sort of special bosses later that I hadn't found yet.
It does admittedly say "Ordinary items" for the drop list, but you wouldn't really find that notable unless knowing normal bosses have boss relics (which aren't ordinary)