Does tremorsense see through the Pass without Trace spell?

Question

The description of the pass without trace spell says:

A veil of shadows and silence radiates from you, masking you and your companions from detection. For the duration, each creature you choose within 30 feet of you (including you) has a +10 bonus to Dexterity (Stealth) checks.

The description of tremorsense says:

A monster with tremorsense can detect and pinpoint the origin of vibrations within a specific radius, provided that the monster and the source of the vibrations are in contact with the same ground or substance.

Say a party of PCs has pass without trace active when they walk through a tunnel where an Umber Hulk has been waiting behind the wall in ambush for prey, using its tremorsense.

Does the Umber Hulk detect the PCs in spite of pass without trace because they are in contact with the floor?

Answer 1

Tremorsense doesn't negate Pass without Trace

Pass without Trace can help in stealth checks against the perception of a creature with Tremorsense.

Is stealth useful against Tremorsense?

The rules of Tremorsense only serve to state that a creature with that ability perceives the world through ground vibrations. What it doesn't do is give it a supernatural ability to perceive all movement around it automatically.

This means it still needs to pit its perception check against a hidden character's stealth check to perceive them, allowing a stealthy enough character to avoid detection.

(As pointed out by Chris Biasbas, this is backed up by Jeremy Crawford on Twitter)

Does Pass without Trace help against Tremorsense?

Pass without Trace says that "A veil of shadows and silence radiates from you[...]". Silence is the absence of sounds and sounds are vibrations. This means that Pass without Trace magically silences the vibrations creatures affected by the spell create. All of this considered it makes sense to rule that Pass without Trace helps in stealth checks against the perception of a creature with Tremorsense.

Answer 2

First we must examine what it does in a more normal situation.

Pass without Trace provides a Stealth Bonus.

It does not provide cover. It does not provide concealment.

If you use Pass without Trace and try to use Stealth while walking through an area with clear line of sight to alert guards, Pass without Trace doesn't let you make a Stealth roll. Stealth only works on foes that cannot clearly see you.

Now, if the guards are not alert (they have no warning of danger, it is late, or they are looking the other way) you can use Stealth.

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Now, how does this apply with Tremorsense. First, it still grants a +10 bonus to Stealth rolls. If we restrict the spell to only doing this (which is quite reasonable), then walking by a creature with Tremorsense waiting in ambush would be akin to walking by an open guard booth with a guard staring into the corridor. No Stealth bonus helps.

If, however, the guard (umber hulk) is distracted the Stealth can help.

On top of that, 5e spell descriptions have no fluff. So while there is no obvious mechanical effect to "veil of shadows and silence" part of the description, you could argue that this means in marginal cases this might make someone less likely to notice you (when they are relying on hearing or bright light to see you). In other situation they might be more likely to see you (a veil of shadows follows you around as you try to hide in a crowd -- the 30' veil might be easier to see than a halfling between the human's legs!)

It comes down to "is the Umber Hulk attentive", and is the "veil of silence" enough to even permit a Stealth check. This is a classic DM's call. Are there other noises that could mask the adventurer's movement? These adventurers going to be quieter than the Umber Hulk would expect (maybe their footsteps sound like small animals), would that matter?

Both calls -- that the Umber Hulk can see the sneaky adventurers clear as day, and that the Umber Hulk is distractible or distracted and has a chance to miss the quiet adventurers -- are reasonable here.

Answer 3

As long as the Umber Hulk and the people with the spell up are in contact with the same ground and are within the radius of the Umber Hulk's tremorsense, then yes the Umber Hulk knows that the party is there. Now if the party isn't in contact with the same ground as the Umber Hulk, then no, the Umber Hulk doesn't know that the party is there if it doesn't see them with another form of sight.