Movement reduction stacking

[stoutstien]

So we have spells that creates difficult terrain and spells that cause movement to cost extra. As far as I know costing extra movement isn't a spell effect so they can stack.
Difficult terrain + plant growth+ wall of sand+ transmute rock?

[Azgeroth]

spell effects do not stack.

so, if you have multiple ' to move x feet you must y movement' do not stack, either the greatest effect takes hold, or the spell of the players choosing.

in the same vein, spells that say 'creatures movement is reduced by x' cannot stack, same as above.

however, you could have one of either affect the same target, i.e. reduce a creatures movement by x, then have movement in an area cost y per 5 ft.

[JackPhoenix]

spell effects do not stack.

so, if you have multiple ' to move x feet you must y movement' do not stack, either the greatest effect takes hold, or the spell of the players choosing.

in the same vein, spells that say 'creatures movement is reduced by x' cannot stack, same as above.

however, you could have one of either affect the same target, i.e. reduce a creatures movement by x, then have movement in an area cost y per 5 ft.

Not true. Effects of the *same* spell cast multiple times doesn't stack. Effects of different spells, even if they are similar in function, do.

[stoutstien]

Not true. Effects of the *same* spell cast multiple times doesn't stack. Effects of different spells, even if they are similar in function, do.
Was my understanding as well. What would the order be? Movement halfed from difficult terrian then one foot costing x 11 if you had all three active?

[Chronos]

The exact wordings matter.

Plant Growth says "A creature moving through the area must spend 4 feet of movement for every 1 foot it moves".

Difficult terrain says "Every foot of movement in difficult terrain costs 1 extra foot. This rule is true even if multiple things in a space count as difficult terrain".

Transmute Rock says "Every foot that a creature moves through the mud costs 4 feet of movement".

Wall of Sand says "A creature... must spend 3 feet of movement for every 1 foot it moves there".

Of these, only difficult terrain modifies the movement cost based on the base movement cost. The other three set the movement cost to a particular value. So if you have both Plant Growth and Transmute Rock, then one spell says that every foot moved costs 4 feet, and the other also says that every foot moved costs 4 feet, and so both spells agree that every foot moved costs 4 feet, and that's what you get. This would disagree with Wall of Sand, but then you resolve that disagreement by saying that the more powerful effect applies, and so it's still a cost of 4 feet of movement for every 1 foot. Finally, if we have some other effect that causes difficult terrain (Spirit Guardians, say), that adds one extra foot to the cost, so now every 1 foot costs 5 feet of movement.

Net effect:
Just difficult terrain: Half speed
Just wall of sand: 1/3 speed
Just wall of sand and difficult terrain: 1/4 speed
Plant growth and/or transmute mud, (wall of sand irrelevant): 1/4 speed
Plant growth and/or transmute mud, (wall of sand irrelevant) plus difficult terrain: 1/5 speed

[Galithar]

The effective spells to stack for movement speed are:

Ray of Frost: Reduces speed by 10 feet until your next turn.
Eldritch Blast (Grasp of Hadar invocation): See Ray of Frost
Spirit Guardians: An effected creatures speed is halved.
Any one of the spells that cause movement to be X feet to move 1 foot.
Any source of difficult terrain. That increases the cost of movement by 1 foot per foot moved.

All together you can get to Movement Speed = (Base Speed - 10 [or 20 if your DM allows Ray of Frost and Grasp of Hadar to stack, RAW they should but not all allow it]) / 2
Then make movement cost up to 5 feet per foot moved.
A creature with speed 30 would become immobilized by standard battle map rules.
30-10=20
20/2=10
10 feet of movement allows the creature to move 5 feet in difficult terrain, or 3.333 or less in wall of sand or similar effect. By RAW battle grid if you have less movement then what is needed to move one square you can't move rendering them immobile.
By stacking the two -10 effects you can immobilize faster creatures and/or do it with fewer effects.

[stoutstien]

The effective spells to stack for movement speed are:

Ray of Frost: Reduces speed by 10 feet until your next turn.
Eldritch Blast (Grasp of Hadar invocation): See Ray of Frost
Spirit Guardians: An effected creatures speed is halved.
Any one of the spells that cause movement to be X feet to move 1 foot.
Any source of difficult terrain. That increases the cost of movement by 1 foot per foot moved.

All together you can get to Movement Speed = (Base Speed - 10 [or 20 if your DM allows Ray of Frost and Grasp of Hadar to stack, RAW they should but not all allow it]) / 2
Then make movement cost up to 5 feet per foot moved.
A creature with speed 30 would become immobilized by standard battle map rules.
30-10=20
20/2=10
10 feet of movement allows the creature to move 5 feet in difficult terrain, or 3.333 or less in wall of sand or similar effect. By RAW battle grid if you have less movement then what is needed to move one square you can't move rendering them immobile.
By stacking the two -10 effects you can immobilize faster creatures and/or do it with fewer effects.
Cant believe i forgot Ray of frost!!
Ok so they stack but are still redundant due to worded to set reduction.

[RSP]

Anything that reduces a character’s speed should stack; anything that sets movement to a new equation (like 1’=4’) would require picking one equation. Similar to how AC works: modifiers can stack, but can only use one equation.

[stoutstien]

Now I want to make a villain that just leechs speed from the partty

[MaxWilson]

Now I want to make a villain that just leechs speed from the partty

Only if you want to make melee specialization feel even more futile than it already does.

(As someone put it recently, I think it was WillieTheDuck paraphrasing someone else, "Paladins are pretty good at everything in 5E except ranged combat, and ranged combat is the most powerful thing in the game.")

[Tanarii]

A creature with speed 30 would become immobilized by standard battle map rules.
30-10=20
20/2=10
10 feet of movement allows the creature to move 5 feet in difficult terrain, or 3.333 or less in wall of sand or similar effect. or possibly 30/2 - 10 = 5ft, reduced to 1 ft in Plant Growth in difficult terrain.

[Chronos]

Huh, I hadn't noticed that Spirit Guardians halves speed directly-- I thought that it created difficult terrain. But double-checking, it looks like you're right.

If I'm not mistaken, this means that even after an enemy gets out of the Spirit Guardians area, they're still moving at half speed. Like, if a creature with 30' move starts off 5' from the edge of the spell, they can only get to 10' away from the edge. By contrast, if it created difficult terrain, then they'd have to spend 10 of their 30 feet to get out, but could then move another 20'.

I'll have to remember to point that out, if it becomes relevant (which it might, because my group includes two clerics, both of whom love that spell).

[stoutstien]

Only if you want to make melee specialization feel even more futile than it already does.

(As someone put it recently, I think it was WillieTheDuck paraphrasing someone else, "Paladins are pretty good at everything in 5E except ranged combat, and ranged combat is the most powerful thing in the game.")
I guess I have never seen ranged combat dominate to a point of making mellee obsolete at a table yet.

[Zalabim]

Huh, I hadn't noticed that Spirit Guardians halves speed directly-- I thought that it created difficult terrain. But double-checking, it looks like you're right.

If I'm not mistaken, this means that even after an enemy gets out of the Spirit Guardians area, they're still moving at half speed. Like, if a creature with 30' move starts off 5' from the edge of the spell, they can only get to 10' away from the edge. By contrast, if it created difficult terrain, then they'd have to spend 10 of their 30 feet to get out, but could then move another 20'.

I'll have to remember to point that out, if it becomes relevant (which it might, because my group includes two clerics, both of whom love that spell).

The technical effect is almost exactly backwards from what you described.

Once a creature leaves the area, their speed is no longer reduced so they can move their full value away, but when approaching the area, as soon as they enter they lose half their speed and may have to stop right there. It's as if all the space they just covered retroactively became difficult terrain.

[ImproperJustice]

Slow also reduces speed by half.

But is that when it takes effect, such as after someone has been hit by a Ray of Frost, or is it applied to base movement first, then you apply RoF?

RE melee types: It’s wise for any warrior to keep a ranged weapon available.

Or be a cool Eldritch Knight that can Misty Step.

[Throne12]

The way I see it you can plant growth to cause difficult terrain them ray of frost.