Does the slow effect affect all attack types?

Question

The Stone Golem has an ability called Slow:

Slow (Recharge 5-6): The golem targets one or more creatures it can see within 10 feet of it. Each target must make a DC 17 Wisdom saving throw against this magic. On a failed save, a target can't use reactions, its speed is halved, and it can't make more than one attack on its turn. In addition, the target can take either an action or a bonus action on its turn, not both. These effects last for 1 minute. A target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

The slow spell has a similar effect.

My immediate thought was that this is aimed at weapon attacks eg. a fighter's extra attack or a monk's flurry of blows. Then I wondered, what about spells that have an attack roll eg. eldritch blast. At higher class levels that spell allows multiple attack rolls. Does the slow effect also prevent you from making the extra attacks with that spell?

What about class abilities like Volley or Whirlwind Attack from the Ranger - Hunter subclass?

Answer 1

Yes

There is a big difference between the Attack action and attack in dnd-5e (see What does upper-case-A-Attack action vs. lower-case-a-attack mean?). The Roll20 version you quote from capitalizes attack in "it can't make more than one attack on its turn"; the Monster Manual (p.170) does not - it is referring to an attack, not the Attack action. Roll20 tends to do this a lot so it should always be double checked with the source - WotC material always says "Attack action" when they mean the Attack action and "attack" when they mean attack.

The Slow effect of the Stone Golem and the Slow spell limits its victims to one attack (PHB p.194):

If there’s ever any question whether something you’re doing counts as an attack, the rule is simple: if you’re making an attack roll, you’re making an attack.

Any features that normally allow multiple attacks, don't. This includes Extra Attack, Flurry of Blows, Eldritch Blast etc.

Except, the official Sage Advice Compendium says that "Whirlwind Attack is unusual, in that it’s a single attack with multiple attack rolls." It has a specific rule that overrides the general rule that each roll is an attack. While it is not in the compendium, Volley should probably be interpreted similarly.

In addition, for the Slow spell, Eldritch Blast (and other spells) are also subject to the rule that they may not come into effect until the caster's next turn.