Looking at Halaster's Light Step (City of Splendors: Waterdeep, p. 154) I was wondering: Would this spell, combined with some form of invisibility, effectively make Blindsight, Blindsense and Tremorsense useless? As well as making Darkstalker somewhat redundant for casters? Or is there something im missing?
First of all, for our purpose, Halaster's Light Step is just like Fly with +10 Circumstance bonus to Move Silently.
The effect on special senses is easily deduced:
- The Move Silently bonus is useless, special senses use Spot vs Hide.
- Tremorsense (regular creature): foiled, as the subject is flying.
- Tremorsense (Aquatic creature): foiled if the subject is flying, not foiled if the subject is immersed.
- Blindsight, Blindsense: not foiled, bats use echo-location for example and locate flying mosquitoes without issue.
Adding Invisibility is useless against special senses, as they do not rely on sight to start with.
So, against Tremorsense, it gives the character a mechanical benefit: by avoiding contact with the ground/liquid, the character does not provoke vibrations which can be picked up.
The comparison to Darkstalker is rather meaningless as well. Darkstalker let you apply your Hide and Move Silently even against creatures whose special senses would normally bypass them; since Halaster's Light Step does not grant such benefits, it's really orthogonal.
Note that a character with the Darkstalker and under the effect of Halaster's Light Step could appreciate the +10 Circumstance bonus to Move Silently.
This does not make the spell useless, however. An invisible caster with +10 Circumstance bonus to Move Silently will be incredibly annoying to locate for the mundane goons; but even without being invisible, simply being able to levitate out of range and not spring up any pressure-based trap is already a great utility. And not falling, of course.
At higher levels, of course, expect pervasive use of Detect Magic/See Invisibility/True Seeing which make magical invisibility much less effective (not even mentioning Mindsight or Lifesense...) and expect enemies with either flight abilities or ranged attack abilities. Then again, it's only a 2nd level spell.