Greetings D&D Beyond,

For the sell Shape Water, one of the options in the spell states:

If an enemy creature is standing near a open container/body of water, and I use Shape Water to cause the water to form a piercing 'icicle' shape as it freezes and it pierces a creature, I have two questions...

1. Should this be an attack roll, or should the creature roll a Saving Throw?
2. How do I calculate the damage for this?

Thank you in advance for the helpful answers :)

Cheers,

The answer is that you cannot use Shape Water to attack a creature.  If you were allowed to make attacks using Shape Water, it would say so in the spell's description.  The most you could do is freeze water into an icicle, then pick it up and hit someone with it, which would count as an improvised weapon (meaning that it would deal 1d4+your strength mod damage, and you wouldn't be able to add your proficiency modifier to the attack roll).

Is the idea you break off one of these icicles and stab someone?

 I’d call it an improvised weapon. No proficiency bonus to attack, just str mod. d4+str for damage.

This is a cantrip with no attack options by RAW. It should be a very weak option if you’re going to repurpose it as such. I’d probably even say you can only use it once before it breaks. I’d really only let you do it because it’s kind of creative, and spending one action, to be able to make a crappy attack on your next action seems like it wouldn’t be unbalanced. 

Strictly speaking, you can't actually cause damage with Shape Water, which is why it's careful in its language with the other options to exclude the ability to do damage.

If you're the DM and decide you want to depart from the intent of the spell, then I'd make that a Dexterity Saving Throw, rather than an attack, because they're avoiding the ice rather than the character targetting the creature per se.

As for damage, I'd go quite low. They're co-opting a non-damage cantrip to do damage, and it's just that the creature happened to hit it. 1d4. If the creature fell on the icicle, then you can add falling damage to that.

Btw creating an ice spike from an open container of water would be two casts of shape water, one to form a water spike, one to freeze it, as shaping and freezing are two seperate effects of which you can only use one per cast.

Quote from Xalthu >>

Is the idea you break off one of these icicles and stab someone?

 I’d call it an improvised weapon. No proficiency bonus to attack, just str mod. d4+str for damage.

This is a cantrip with no attack options by RAW. It should be a very weak option if you’re going to repurpose it as such. I’d probably even say you can only use it once before it breaks. I’d really only let you do it because it’s kind of creative, and spending one action, to be able to make a crappy attack on your next action seems like it wouldn’t be unbalanced. 

 I agree with everyone here but I also like this post. I think I would take this route as well. It is no different than picking up a rock and throwing it, only it requires more steps (having water and then shaping it into something that can be thrown, then throwing it on the next action). Given the inherent penalties in the desired action that make it worse than using a rock, I would allow it because it is kind of creative.

Casters man, they always gotta complicate things to be flashy. :P