Lovely game. I really enjoyed playing it! <3 Keep up the great word :) Two quick ideas for potential achievements:
a) "strike at the heart" - mine 60 core fragments in one run (possible with the shield stack sigil and enough power and stamina. Not super hard when using the sigil, but impossible otherwise i think)
b) "lightning speed" - reach water within 60seconds (can be done in 27secs using griddle, the vermilion pickaxe, the rollerskates for the extra stamina, the violetheart pendant and the regen+1 sigil. A bit of luck, ripping the double flask on the descend and holding downwards will do the trick)