18.104.22.168, 22.214.171.124, 126.96.36.199 Hotfix
The achievement requires that you "Hit each type of underwater mob with the fishing rod."
- Drowned vine man
- Drowned skeleton
- Drowned zombie
- Drowned Necromancer (WHICH YOU CAN'T HIT)
- Drowned slime
- Glowing squid (found at the end of secret level Raviant ravine )
The achievement is bugged because since the last update you are unable to "hit" the necromancer. Your rod will ignore it completely or will just go through it.