Here is the full list of all 49 Grindstone achievements.
Create a 30-Chain Grindstone
Complete Level 1
Create a 15-Chain Grindstone
Kill 1000 Creeps
Kill 10000 Creeps
Survived your first boss
Defeat SkjellyKjing
Defeat Creepzïlla
Defeat MekkaMortie
Defeat Jjurk-Creepethuth
Defeat MjeatBöll
Survived Jjary, again (and again and again)
Complete 3 Creep hideouts
Create a 45-Chain Grindstone
Complete a Greed Grind without dying
Complete a Quick Grind without dying
Complete a Fortune Grind without dying
Kill 5 Slobs
Kill 50 Slobs
Kill 20 Jerks
Kill 200 Jerks
Start a level with only 1 heart
Wake up in the Inn
Eat 3 of Helgä's snack items
Spare a Royal Slob
Collect 1000 grindstones
Collect 50 guts
Collect 50 wood
Collect 50 iron
Collect 50 batwings
Collect 50 bones
Collect 50 ectoplasm
Collect 50 ice
Collect 50 magma rocks
Collect 50 poison mushrooms
Collect 50 Vine Hjeart seeds
Collect 50 crowns
Collect 50 gold
Use the OK Boomerang over lava
Cause a Jerk to die from poison
Dodge 3 attacks with the Gladiator Outfit
Make a Jerk melee another Jerk
Mine gold using the Goldrush Garb and Pickaxe
Complete a level with the Spinny Sword, Arrow, and Pickaxe
Complete a level with any 3 pieces of gold gear and the Grindstone Garb
Complete a level with the Ranger Outfit and any 3 arrow types equipped.
Complete a level with the Vine Sword, Poison Arrow, Poison Shield, and Plague Doc Outfit
Complete a level with the Detonator Suit, Fireball Sword, Fire Arrow, and Firewalker Potion
Unlock all other achievements