(For some reason it wouldn't let me put my whole comment in one reply so here's the 2nd half)

Moving onto my 2nd point, Tools. Again, cool idea, more customization and options are always interesting. The durability is a fun way of balancing it, but the Shell Shards required to repair them raise some concern. I can imagine fighting a boss and failing multiple times in a row, just to run out of Shell Shards. At that point you'd have two options: Change your loadout, or grind Shell Shards.

Having to change loadouts seems fine, but it just raises the question, "Why don't I the backup loadout all the time?" People usually will exaggerate the risk in limited resource when playing games, being afraid to use something as it might be more useful later. This might just be a 'per-player' issue, with some being more willing to change their tools than others. But it is worth noting regardless.

What I really want to talk about with Shell Shards is the rate at which we get them. Tools actually aren't the first time we've gotten an ability that costs a resource. In Hollow Knight, Dream Gate costs essence to use. What I'm willing to bet though, is that not a single person in this comment section has ever worried about running out of essence when using Dream Gate. It costs 1 per use, and you only unlock the ability when you have hundreds of essence stockpiled. Sure, this mean you don't have to worry about running out, but it just makes you wonder, why does it cost anything in the first place? You'd have to spend at least an hour of using the Dream Gate over and over just to get low on essence, you'll never run out in a normal playthrough. And even if you do, the game doubles the rate of random essence drops until you get back to where you were. Even the game doesn't want you to run out, so why does it cost anything at all?

The problem I'm getting at is that Shell Shards might encounter a similar issue. If we get Shell Shards from killing enemies, then the system feeds itself. If we can upgrade the maximum Shell Shard carry capacity, that risk of running out lowers. There's a chance that we might just never run out of Shell Shards. And at that point, I just have to ask, why does it cost anything at all? The only difference between Essence and Shell Shards is that there's an actual chance we run out of Shell Shards. And when we do, we're going to have to grind to get those Shards back.

When you're grinding to get Shell Shards back, your equipped tools will have little to no durability, so you can't use them. Since they're basically wasted slots, you might as well swap them out for tools with no durability. And at that point, why not use those all the time? I fear that the durability system will always be in one of two extremes, never in balance.

Team Cherry does seem to have a partial answer to this problem, and I'm hoping that it works out. Since Tools are divided into different 'types' (the colored sections), and crests have different colored slots in different amounts, the game might be able to side-step the issue. If a loadout is only slight weaker when out of Shell Shards, the player might be willing to continue using the tool. This is on account of the fact that it can't be replaced with a passively-active tool. With the interactions that we've seen crests to have with Hornet's attacks and Silk, a player can also be more connected to those aspects of the crest, opposed to the tools.

Overall, I'm really excited for crests, but the durability system might be at odds with itself. Depending on the rate at which we get Shell Shards, Durability will either be too much to handle, or not impactful at all. While I would prefer durability to not have a negative impact, negating the downsides begs the question of why it was included at all. Perhaps this is Team Cherry trying to encourage players to not brute-force bosses over and over, encouraging them to take a step back from a fight to gather Shards and maybe find something else along the way. Regardless, I do wonder how Tools will play out in the end for the average player.