In my last session, I pit my party against a demilich. The demilich has a movement speed like so: “Speed 0 ft., fly 30 ft. (hover)”
During this combat, the party's druid summoned pixies and used one of them to cast Entangle on it. Entangle reads like this:
Grasping weeds and vines sprout from the ground in a 20-foot square starting from a point within range. For the duration, these plants turn the ground in the area into difficult terrain.
A creature in the area when you cast the spell must succeed on a Strength saving throw or be restrained by the entangling plants until the spell ends. A creature restrained by the plants can use its action to make a Strength check against your spell save DC. On a success, it frees itself.
When the spell ends, the conjured plants wilt away.
Can a hovering creature actually be affected by Entangle?
I personally wasn't sold on the idea that a flying/hovering creature could be effected by Entangle's restraining effects. It seems to me that if the plants were capable of growing enough to reach a flying/hovering creature, there wouldn't be much chance to succeed the STR saving throw, as the plants could easily be above the creature's head on all sides.
I let my player have his moment as it didn't much effect many of the demilich's abilities, but I was curious if anyone had some info on this.
Best Answer
RAW is unclear, but likely not
Neither square or hover are clearly defined terms but from their context we can draw decent conclusions.
A hovering creature is still flying and would not be within the 2-D area of effect for entangle.
Entangle's Area of Effect
The area of effect for entangle is a 20-foot square. Square is not one of the shapes listed in the PHB section on areas of effect (PHB, p. 204). The DMG only mentions it as "Cube or Square" when determining the number of creatures within an area for gridless play (DMG, p. 249). Additionally, both the PHB and the DMG are fairly light on 3-dimensional rules like height for things other than cubes, spheres and cylinders.
In contrast the spell web has an area of effect of a 20-foot cube when anchored. Without anchors its area is describe as:
We don't have a rule for how high the area of effect for entangle reaches, and therefore how high the demilich would need to be to avoid it.
In my interpretation, square is a 2-dimensional version of cube, therefore it has no height and a creature must be on the ground in the area to be effected. Therefore unless the demilich is touching the ground (which it doesn't need to) it should not be affected.
Hover ability
From the Flying Movement section under Movement and Position (PHB, p. 191) we have the meaning of "hover" (emphasis mine):
The demilich's hover ability prevents it from falling when knocked prone, but otherwise has no effect on area of effect for spells like entangle. It does mean that the demilich can choose to be at any height without fear of touching the ground; however, other than that, it obeys the regular rules for flight.
To clear up confusion, hover is a more powerful version of flight, not less. Would you rule that a creature flying 5ft above the ground is effected by entangle? I would rule that it is not. So a hovering creature would not be effected either.