**Gradually increase the drop chance of an item every time it *doesn’t* drop**
The worst part of grinding for a specific item in Terraria is that no matter how long you grind without getting the drop, you are no closer to receiving the item than when you started, despite the gambler’s fallacy. This makes grinding, in my opinion, quite excruciating.
To solve this, you could make the base drop chance of any random drop lower, but gradually increase the drop chance every time it doesn’t drop, and when it finally drops, reset the chance to its base value. This can apply to enemy drops, boss drops, and fishing, and maybe even other random factors like traveling merchant shop.
This will make grinding somewhat less excruciating, because even if it doesn’t drop, you know that the chances are higher next time.
I haven’t gotten into Terraria modding, so I don’t know how difficult this would be. However, drop chances clearly can be changed dynamically at runtime, as with the Defiled Rune. Ideally, it would be okay to apply the same general rule to every random item drop (ex. Halve every drop chance, and make it increase by 15% every time it doesn’t drop), instead of fine-tuning for each item.
Also, I am not sure whether this should apply per player (if that is even possible) or per world. I always play cooperatively with friends, and we share loot, so I would personally be okay the changes not applying per player. However, I understand it could be very frustrating if another player gets the drop you were grinding for, resetting the odds. If the drop chance applied per-player, it could solve this issue.
Also, I understand, it would negatively impact the loot of defeating a boss for the first time if the base drop chances were decreased across the board, so perhaps boss drop chances should begin at their unmodified value, and only reset to their lower base value when the item is dropped.
(I came up with this idea when I was grinding for a compass for cell phone)