Underwater Communication
The needle spitter penis fishes were weak to slashing and magical attacks, however, smashing weapons couldn't damage them. Because of this, Ashardalon had to store his shield in his space bag and took a two-hand sword that he kept inside his bag for situations like this, where his shield is ineffective.
If it was in the dry land, Ashardalon could smash it to the ground. In this way, even monsters immune to smashing damage can be crushed to death. But it is impossible in the water, not just because of the reduced speed that enables the monster to escape before the process end, but also because the players didn't walk on the seafloor. If players are swimming, it will be difficult to crush the monsters on a hard surface.
Players can use their creativity to smash marine monsters on underwater cave walls to deal damage but it is hard to achieve and even harder to do it repeatedly to do constant damage.