Does using Mold Earth to trip someone break its rule against causing damage?

Question

I have read this part of the Mold Earth as allowing a trip effect:

• If you target an area of loose earth, you can instantaneously excavate it, move it along the ground, and deposit it up to 5 feet away. This movement doesn’t have enough force to cause damage.

The save is a Dexterity save against the spellcaster's Save DC or be knocked Prone. I had ruled that Huge and larger creatures cannot be tripped this way, and that Large creatures and creatures with more than two legs have Advantage on the save.

It seemed clever the first time it was used but now it creates problems with encounters — the Wizard simply Readies the spell until after the intended target's turn, and releases it with his high Spell DC (15- he has 20 Int at level 1). This allows the party members to attack with Advantage for the whole round.

Does tripping the enemy in this way violate the limitation of force exerted by the spell?

Answer 1

Well done!

Congratulations to your player in coming up with an imaginative use for the spell. Congratulations to you for enabling it and working out simple, practical mechanics for it.

I personally would have made it a Dexterity (Acrobatics) ability check rather than a saving throw as it is an attempt to keep your balance rather then actually resist the spell and also because more creatures have proficiency in Acrobatics than Dexterity saving throws. I would also consider Strength (Athletics) to stand your ground and give the target the choice.

I would also rule that creatures with other than 2 legs get advantage due to their greater stability.

Is this OP?

Does it break the rule about causing damage? Clearly not.

However, what I think you are asking is: is this overpowered for a cantrip?

My take is probably not and here's why:

• The wizard is giving up their action to possibly knock a single enemy prone. This means they are not using that action for something else like casting a higher level spell or a different cantrip. The chance is 70% for a modifier of 0 on the roll (going down by 5% for each +1).
• If the wizard instead used their action to Help they would guarantee advantage for one of their companions.
• "Fool me once shame on you, fool me twice shame on me". Guess who the creature is targeting next round, you know, while the wizard is concentrating on the Mold Earth cantrip? With a ready action, the caster is concentrating on the spell from their turn up to the trigger point.
• Anyone with a decent Strength (Athletics) modifier can do this as one of their attacks in an Attack action. If they have the same modifier they are better than the wizard (77.25%) and they are even better as the opponent's modifier increases. If they have multiple attacks, they can do this and still attack themselves.
• Don't even get me started on someone with expertise in Strength (Athletics) and the Shield Master feat. Grapple, knock prone with a bonus and they can't get up because their movement is 0.

Deeper concerns

Readying action requires you to "decide what perceivable circumstance will trigger your reaction." That is perceivable to the character. "When it completes its turn" is perceivable to the player, not the character.

I'm not saying it can't be done, I'm just saying it can't be done with that trigger.

"When it attacks, moves or casts a spell" is a workable trigger but there is the possibility that it does none of those things and the wizard is left with nothing to hang their action on.

Answer 2

No, it does not violate the rule against the spell causing damage, because the spell is not causing damage. The other PCs are causing damage (as is their right) after the spell has knocked an enemy prone. I tend to agree with Dale that this is a perfectly valid and creative use for the spell, nor am I concerned about it being overpowered in any way.

If the wizard is doing this all the damn time and you just want to mix it up a bit, there are still some things you can do:

1. You could throw encounters at them where the monsters have natural bonuses to avoid the effect (ie: large size, multiple legs) as you've already established they have bonuses against it. Still throw SOME regular encounters their way though - nothing more annoying, as a player, than finding a sweet combo and suddenly EVERY ENCOUNTER IS BUILT TO DEFEAT IT.
2. You could have a few adventures indoors or underground, ie: places where there isn't a substantial amount of "loose earth" (which the spell requires in order to work.)
3. As a cantrip, it shouldn't take much in the way of antimagic/spell resistance/counterspelling to overcome this one.
4. One of my personal faves: give the enemy group a spellcaster and have him do the same thing to the party.
5. Two words: Displacer Beasts! (or similar illusion magic for other creatures.) The party wizard can't trip an enemy if he's not 100% sure where their feet actually are.