Interesting use of Water Walk

[Sadras]

So the characters, all 5th level, undertook a quest to deal with a water elemental that was attacking the barges, as well as other smaller vessels sailing up the Windrush River. Reports indicated that the elemental focused its attacks on the vessels rather than the passengers unless it was attacked. Preferring to capsize, sink and pull the vessels apart and have the people flee towards the embankments, rather than engage in combat.

The players mulled over how they would deal with such a threat as the water elemental could always just hide within the deeper waters of the river, striking when needed. The player of the druid character came up with an interesting idea - casting Water Walk on the elemental.

It required a house ruling from me, given than the spell stipulates willing targets and no save. I ruled that the elemental, being an unwilling target, would receive a strength saving throw to resist the spell's effect. Selected strength, given the forceful movement.

If you target a creature submerged in a liquid, the spell carries the target to the surface of the liquid at a rate of 60 feet per round.

If the elemental fails its saving throw, the spell effects automatically force it 60 feet up towards the surface, but that does not mean the elemental can not use its swim 90' to outstrip the spell's effects. The duration of the spell is an hour, no concentration.

I do not believe the players have thought about the movement action available to the water elemental so I imagine it will come as a surprise to have the spell not work as well as they'd hoped.

The druid's secondary 3rd spell is Water Breathing for obvious purposes.

EDIT: Interestingly the spell Levitate uses constitution as the ability choice for the saving throw. Gonna have to give this some thought.
Levitate has a duration of 10 minutes, with concentration, but the spell does not seem to permit flight movement, only pushing and pulling, whereas Water Walk has no such rider given that the spell was written for willing targets.

 

[Blue]

For me, the "willing target" is a clear sign of intent, so I wouldn't allow it at my table.

If I was did allow it, I'd "convert" the hostile use to match other spells on unwilling targets. Primary is it would require concentration. I'd would still keep it at a single save instead of a save every round, just looking at the effects of which spells require every round it doesn't fit that category.

 

[Satyrn]

Neat idea.

Were I DMing, I might be tempted to tell the player that requires researching a new spell. Well, "research." It's a druid so I'm thinking it would entail a few days meditating in a grove, inhaling various expensive varities of "incense." Probably ( one day and X gold) per spell level.

The party would then have to decide if leaving the river open to attack for a few days was worth the risk for this benefit.

 

[77IM]

I'd allow this, but only if the caster can succeed on a DC 13 Intelligence check during casting; on a failure, the spell slot is wasted.

That's my general go-to when a player wants to break a spell rule, or any rule, really. Make an ability check, and on a success the player gets what they want, and on a failure they lose something or wind up slightly worse off. (Nothing terrible, just a reasonable deterrent so people don't try this on every single casting.) And it's only an ability check -- no proficiency applies because a) the probabilities are tighter on a raw ability check and b) proficiency is for things that you can definitely do and have practiced, while this sort of check is for improvised moves that by definition you haven't tried before.