You can craft the Bastion Bow once you get the green stone off of a green stone you can use your hammer on or randomly dropped bya blue pot where you ususally find sea shards in.
After you crafted the bow, you have to use a fully charged shot on a „soft“ ground. So it doesnt work on rocks. You can see a green sphere where the damage you take is
Be sure to have as low health as possible since the fall damage in this game is pretty low. Now jump into the green sphere from a tower or something high enough and the achievement should unlock immediately.