Does the Horde Breaker feature work on the attack granted by Haste?

Question

The haste spell, as well as the Potion of Speed which mimics it, grants an additional attack on each of the creature's turns. The wording says "one weapon attack only", but...

There's a 3rd-level Hunter ranger feature called Horde Breaker that allows the ranger to make one additional attack (with the same weapon, against another target) when he makes a weapon attack. So...

Let's say a ranger drinks a Potion of Speed as his action, then attacks with the additional attack from haste. Would he then be able to benefit from Horde Breaker and make an additional attack?

Answer 1

Yes, you can use horde breaker with the Attack granted by haste

Horde Breaker says:

Once on each of your turns when you make a weapon attack, you can make another attack with the same weapon against a different creature...

Since haste grants the ability to make one weapon attack as part of an Attack action, it will definitely be a valid trigger for the Horde Breaker ability.

This will work even though haste specifies that the Attack action can be used to take only one weapon attack, because the Horde Breaker attack is not made as part of that Attack action. It just happens to be triggered by that action, so it does not violate that stipulation.

So, because the haste attack is a weapon attack, you can use Horde Breaker to make an additional attack.

A couple things to note though:

• Horde Breaker can only be used once per turn no matter what features you use to trigger it.
  • This means that if you take the Attack action normally and make an attack, then use haste to take the Attack action again and make another attack, you cannot get an additional Horde Breaker attack with both attacks - only one (per turn).
• The horde breaker attack must use the same weapon and target a different creature within 5 feet of the original target.

Answer 2

It can, but Horde Breaker is done outside of Attack or attack actions, and can only be used once

Horde Breaker requires (emphasis mine):

Once on each of your turns when you make a weapon attack, you can make another attack with the same weapon against a different creature...

The Horde Breaker has three stipulations: 1. The option to use this can only happen if you first make an attack with a weapon 2. You must use the same weapon you attacked with when you use Horde Breaker 3. You can only use it once per turn and only when it's your turn.

Haste and Horde Breaker

Haste grants (amongst other options) you another single Attack. If you haven't yet used Horde Breaker and you use the Haste action to attack with a weapon, then you can use your Horde Breaker after that.