The Mysterious Circuits were originally supposed to be something very different. REALLY early on in development the idea of unidentified items came up, and I discussed it with Chris a lot. NORMALLY, I loathe the mechanic, but I knew of a game (Baroque, on the Wii and PS2, basically the game that got me into the roguelike genre in the first place) that did it in what I thought to be the RIGHT way, so I'd wanted to do a similar system here.
Of course, the items as a whole evolved in a very different direction, and thus the concept was mostly thrown out, but the Circuits are a leftover relic of that mechanic. The final version of the circuits is almost identical to how Isaac's pills work (at the most basic level, anyway), as Logorouge mentions. I don't remember whose idea that bit was. But yeah, they didn't come out all that well... nowhere near as refined as Isaac's.
As it is, there are a few reasons why Isaac's pills work, VS what is wrong with these.
1. In Isaac, there is a very large number of different pills, however a huge part of why they work is that each time you start a new run, a small set of pills is randomly chosen out of that overall list, and only those pills appear during the run. The pill selection in each run is usually pretty even... there are good pills, bad pills, and pills that are sort of neutral or somehow just screwy (like one that takes the number of bombs and keys you have, and switches them... it's not "good" or "bad", but it can help, or it can hurt, depending on the situation). I think this system of selection is a huge part of why Isaac's pills work as well as they do.
2. Pills in Isaac are very common. You're going to encounter lots of them on each run, and there are all sorts of items that can influence how many you find, and even active items that can just keep spawning more for you. So if you're having a run where you know you've got a particularly good set of pills available, you can try to go for items that then improve your chances of getting even more. Pills are frequent finds in normal rooms, sometimes they're a room reward, and almost all shops will have a random pill for sale.
3. There are items that can influence pills in different ways. For instance, the PHD item alters the run's current selection of pills, removing all negative ones and instead having mostly positive with a couple of neutrals, and it identifies all of them for the rest of the run. This item can actually be found in shops, making it a little easier to get than if it were in any other pool. Or you might have something that can perhaps reroll pickups (anything like hearts, keys, coins, pills, cards, all of those are pickups) into other things. You have a lot of options with these, and pills are a major game mechanic, not something that sits on the side.
4. Pill effects range from weak but noticeable, to very strong. One pill for instance can will give you three blue flies... little familiars that seek out enemies, and crash into them, doing solid damage but dying in the process. Just 3 blue flies isn't a very strong effect by itself, but it's still noticeable and you're always glad to have some. Whereas strong ones might do things like increase your fire rate or other stats permanently, give a heart container, or spawn numerous soul hearts (special hearts that allow you to extend your HP past it's maximum). Negative ones are similar in terms of how weak or strong they can be. A weak one might paralyze you for 3 seconds... not too bad. A nasty one might permanently lower your fire rate, or destroy your minimap for the rest of the level (basically the most bloody irritating thing in the game, as far as I'm concerned... let's NOT do that one).
5. The list of pills overall is pretty well balanced. It's clear that a lot of thought went into these.
6. The list of pills is LONG. Can be seen here, if you're interested:
https://bindingofisaacrebirth.gamepedia.com/Pills Over 40 of the things if you have both expansions... that's quite a lot. If you're playing Rebirth by itself, each run will contain 9 pills from that list. If you have Afterbirth, it is upped to 13. Pill colors are randomly assigned, of course. The nice thing about all of them from a design standpoint is that none of the effects they produce are actually complicated... they really don't need to be.
Whereas the similar mechanic in Starward doesn't really have these aspects. It's very clearly an unfinished part of the game, but I'd really love to improve it and encourage players to use them.
I always wanted some weapons that were related to bosses (attack patterns from bosses) but I never really understood how the whole scripting language worked to do that.
It would be cool if each of the perfect boss achievements would unlock a weapon that was inspired by the related boss. Weapon atterns that are similiar to the boss and such stuff.
An example would be, we could make the V-/arrow-like shot from Crystal mother (the green one) as attack with reduced size.
Another idea would be, if you beat the game with an incredibility, you unlock a more powerful version of it.
Yeah, some boss-inspired items/whatever are coming. Looks like I'm going to be making some of them myself.... that should be "interesting". I'll try not to break anything. Keyword there is "try". But I'm excited to give it a go.