The Pacifist achievement is one of the more annoying achievements in Capsized. The achievement conditions are to fire no bullets, this however does not mean 0 kills. Despite being called Pacifist you can kill as many enemies as you want as long as you do it using your gravity hook to hurl rocks at enemies or throw enemies at walls. As long as you reach the end of the stage and it says 0 shots fired the level will count.
The gravity hook: This is what lets you do pacifist, use it to pick up rocks and chuck them at enemies. A strategy I liked to use for some enemies is to hold onto the rock and use the scroll wheel button to "fire" the rock but have it still stay near me. This is useful for not shooting your rock away when you might be surrounded by enemies.

Level 1-3 are pretty straightforward, mainly just pick up a rock and blast anything you meet, you shouldn't run out of lives before you finish.
1 you can rush through without caring about what the enemies do.
2. head left into the pit with the flowers and metroid things, use the rock to kill anything you meet, bring it with you for majority of the map.
3. You're gonna want to head down first since you need to clear some debris at the bottom to proceed to the end. Otherwise just kill everything with rocks again.

Level 4 and 5 are much much harder than the first 3, however if you try to do pacifist on any other stage it will be a nightmare.
The most important part of level 4 and 5 is to pick up the blue orbs in the stage instead of using rocks
These blue orbs will basically one shot anything you throw them at and have some odd explosion mechanics where it will do splash damage.

In level 4, you will find this orb under the wooden bridge immediately at the start. My suggestion is you do the statues in order of top left, bottom right, middle, and top right. There is another blue orb near the middle statue so after the bottom right statue you can abandon your first orb without having to try and shoot it up.

In level 5, the orb is once again near the beginning. When you get the orb try to prevent it from falling down below the bridge. You're going to wanna save the rightmost crewmate first simply because its easier to drop the orb than fly all the way back up. After you save the right crew member make your way back to the bridge and then go down to save the other two crew members. Avoid going too far right as there are a lot of enemies over there and no crewmates to save over there.