When I realized I lost my 100% badge for this game, I wanted to get it back. After realizing there are barely any visual guides about how to get to suicide island, I wanted to make one just so people know what to look out for. The achievement isn't the hardest to get, but it sure is a hassle and a time consumer. So, I hope this will help you get the achievement!

For some odd reason, this is the easiest step.
Sail all the way to the corner of the map, progressing your characters and ships as normal. Once you reach the corner, here you will have to fight a legendary pirate. Win the fight and move on to the next step

Due to the RNG nature of town generation, this can take quite a while. So, while you are sailing to defeat the legendary pirates, I recommend checking out every town you come across. Once you finally find the witch, buy all the Arsenic you need for your crew. (If you have 40 crewmates, you need 40 arsenics). After this you are on to the next step!

Same as with the Witch, due to RNG this can take a long while. Keep an eye out while traversing the waters and spend points on map reading and map awareness. In case you dont know what suicide island looks like on the map, see the attached picture

Once you reach Suicide island, you will talk to the guy on the island, commit suicide, reach hell and then you will have to fight 15 waves of increasingly bigger and stronger groups of skeletons. At the end of this, if you survived, your achievement should pop.

It could be that some of you are just here to get your 100% game back and you dont want to go through the hassle of relearning the game or that you have struggled too much and want an easier solution. For that, there are cheats in the game. You can follow the following guide by JDawg147 to learn how to use the cheats: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=318342741