Im not sure how the Diamond pickaxe is unlocked, I completed everything in the game aside from unlocking it within a day or so, its a very cute and entertaining use of a day.
I also encountered a minor bug on the browser version of the game, when wearing the crystal circlet and afking for a little to scroll the comments, I found when id scrolled up that the effect from the headgear had "overlapped" many times and it dropped the framerate immensely until I refreshed the page.
Making games is really hard, and making one that balances progression and entertainment with a rougelike mechanic is even harder, especially in later game. this one did a very good job so congratulations ^^
I really liked the Variety and gameplay changes between each character, some creative twists on the simple mechanics really did shake things up, Fern and Griddle really stand out as their quirks completely changed the method you'd approach the digging and the preferred gear.
one thing that would be nice to see, from a completionism point of view at least, would be more achievements for tasks done, such as unlocking all the characters then headgear/tools/upgrades etc- not a necessity but as it stands the achievement tab only having two achievements is underutilising the mechanism.
another thing, it took me scrolling through the comments to realise how to unlock Nix, maybe I'm slow but it wasn't clear that Quartz doesn't spawn in that zone (maybe because the zones before it gets dark around the ice level all have Quartz, so I assumed it spawned and I couldn't see it?) so I kept doing multiple runs searching for it to spawn.