The movement_speed attribute has no effect on flying mobs

flying or swimming is still a movement, which is what the attribute name implies it should modify - movement speeds, it isn't titled walkingSpeed, so I do not see this as intended.

Reopened and gave the ticket to Anthoni Wiese. Please update the list of affected versions, title and description to accurately reflect the issue as it in current versions.

True, same for speed/slowness potion effect then as well (which I saw get resolved by that reason if I remember correctly)

Confirmed for 15w51b/latest 1.9 Snapshot.
generic.movementSpeed still not working.

I tested this command in 15w51b, without success (Bat is still moving normally fast):

summon Bat ~ ~ ~ {Tags:[LLPartShow,PartBat],Attributes:[{Name:generic.movementSpeed,Base:0.05}],Invulnerable:1,Silent:1,ActiveEffects:[{Id:14,Amplifier:0,Duration:630720000,ShowParticles:0b}]}

Kind regards, Meri

I can confirm it still not working in 15w51b, added it to the affected versions list. I am still keeping tabs on this particular report.

A slight change to the bat's hard-coded movement speed multiplier (class EntityBat, method updateAITasks) seemed to work pretty well. Original section via MCP:

this.motionX += (Math.signum(var3) * 0.5D - this.motionX) * 0.10000000149011612D;
this.motionY += (Math.signum(var5) * 0.699999988079071D - this.motionY) * 0.10000000149011612D;
this.motionZ += (Math.signum(var7) * 0.5D - this.motionZ) * 0.10000000149011612D;

Modified:

double movementSpeed = this.getEntityAttribute(SharedMonsterAttributes.movementSpeed).getAttributeValue();

this.motionX += (Math.signum(var3) * 0.5D - this.motionX) * movementSpeed;
this.motionY += (Math.signum(var5) * 0.699999988079071D - this.motionY) * movementSpeed;
this.motionZ += (Math.signum(var7) * 0.5D - this.motionZ) * movementSpeed;

While upon instantiation its default would be set to the original multiplier (method applyEntityAttributes):

this.getEntityAttribute(SharedMonsterAttributes.movementSpeed).setBaseValue(0.10000000149011612D);

For ghasts, I did the same (class EntityGhast, method onUpdateMoveHelper). Original:

this.field_179927_g.motionX += var1 / var7 * 0.1D;
this.field_179927_g.motionY += var3 / var7 * 0.1D;
this.field_179927_g.motionZ += var5 / var7 * 0.1D;

Modified:

double movementSpeed = this.field_179927_g.getEntityAttribute(SharedMonsterAttributes.movementSpeed).getAttributeValue();

this.field_179927_g.motionX += var1 / var7 * movementSpeed;
this.field_179927_g.motionY += var3 / var7 * movementSpeed;
this.field_179927_g.motionZ += var5 / var7 * movementSpeed;

Attribute instantiation (method applyEntityAttributes):

this.getEntityAttribute(SharedMonsterAttributes.movementSpeed).setBaseValue(0.1D);

Both seemed to work fine with no obvious issues. Able to change their movementSpeed attribute and see the changes take place (such as a value of 0.0 preventing movement), and the /effect command can successfully modify their movementSpeed.

Can confirm this issue still exists in 16w03a and 16w04a snapshots. Updated the versions list for this, and fixed an issue in the description saying to compare the skeletons instead of ghasts.

Confirmed for pre-2.

Posting to confirm for ghasts and bats in 1.11.2. Neither movementSpeed or speed/slowness effect/potions will alter their movement speeds:

/summon bat ~ ~1 ~ {Attributes:[{Name:generic.movementSpeed,Base:0.001}]}
/summon bat ~ ~1 ~ {ActiveEffects:[{Id:2,Amplifier:5,Duration:19980,ShowParticles:0b}]}
/summon ghast ~ ~1 ~ {Attributes:[{Name:generic.movementSpeed,Base:0.001}]}
/summon ghast ~ ~1 ~ {ActiveEffects:[{Id:2,Amplifier:5,Duration:19980,ShowParticles:0b}]}

Oddly, it seems to work for blazes, but only when they're "walking" (touching the ground)

Confirmed for 17w13a (and 1.12-pre3).

Confirmed for 1.12-pre7 (already added)

@unknown, you don't have to comment when you add affected version(s) yourself

I may not need to SunCat but not everyone looks at the activity logs, or sees the full version list and may repeat whats already been added.

Affects 1.12.1 (and 1.12.2)

Confirmed for 1.13.1.

Confirmed for 19w04b.

Confirmed for 1.15.2 with the above command, and also with the following command:

/effect give @e[type=ghast,limit=1,sort=nearest] slowness 30 7

Can confirm in 20w48a.

Can confirm in 20w51a.

Can confirm in 21w03a.

Can confirm in 21w05b.

Can confirm in 21w06a.

Can confirm in 21w07a. Video attached.

Can confirm in 21w11a.

Can confirm in 21w14a.

Can confirm in 21w17a.

Can confirm in 1.17.

Can confirm in 1.17.1.

Can confirm in 22w13a. This also now affects the allay.

Can confirm in 1.19.2.