This material makes a character capable of breathing underwater, so DMs should take note of that fact. Situations which assume that the character must resurface to breathe, lest they suffocate and drown, may not be significant challenges to a character using this material. Challenges of these sorts are, however, an excellent tool to highlight the character's advantage. One should be cautious to include challenges which are actually capable of threatening such a character regularly; such as boiling/freezing water; poisonous/acidic/contaminated water; aquatic monsters; moving water which would sweep the character away to a pre-planned destination; liquid barriers composed of something other than water, such as oil, blood, soup, or magma; or stagnant water devoid of meaningful oxygen supply; but without punishing the player or coming across as a gimmick. Be careful about who is allowed to use this material, as immature players will likely abuse this to derail the campaign. As should be standard, such players should be dealt with outside-of-game through open communication, but it is often best to avoid the situation in the first place. New players often have difficulties visualizing themselves as another person, let alone another creature capable of living in environments that they themselves will never experience. As such, if a new player is allowed to use this material, they may need some degree of guidance to remember that their character can hang out under water indefinitely, though it should only take a few sessions to really drive the point home.