How does haste interact with the heavy armor penalty?

For a character that is wearing heavy armor, but does not have the prerequisite strength, there is a 10ft speed penalty.

If the Armor table shows “Str 13” or “Str 15” in the Strength column for an armor type, the armor reduces the wearer’s speed by 10 feet unless the wearer has a Strength score equal to or higher than the listed score.

Haste doubles the speed of the person it was cast on.

Until the spell ends, the target’s speed is doubled

Since the movement speed of heavy armor is a fixed amount, does the doubling apply to the base speed or the current speed? ie. A human with a base speed of 30. They put on heavy armor and have their speed reduced to 20. Haste is cast on them, does their speed become 30*2 – 10 = 50 or (30-10)*2=40?

Can I use the haste action to break free of vines or similar things?

Haste states:

Choose a willing creature that you can see within range. Until the spell ends, […] it gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

This obviously does not allow to use any other actions that you can usually use, like casting a spell, as the more specific rule beats the general rule of what actions can be used. But what if some other specific effect grants additional option to use an action for? For example say an Assassin Vine has entangled me, that grants me the additional action option of breaking free from the vines:

A creature restrained by the plants can use its action to make a DC 13 Strength (Athletics) check, freeing itself on a successful check.

Can I use my haste action to try to break free?

As far as I can tell, I have two specific rules contradicting each other. If there is no official ruling on this, does anyone know what be ruled in AL?

How does Mythic Haste interact with 1 round spells?

Mythic Haste states:

Affected creatures gain an additional move action each round.

The rules for casting spells state:

A spell that takes 1 round to cast is a full-round action. It comes into effect just before the beginning of your turn in the round after you began casting the spell. You then act normally after the spell is completed.

If I cast a 1 round spell before using my move action, does the spell finish early?

Can I break concentration with Haste, before it ends, by casting another concentration spell? [duplicate]

Example:

Turn 1: Cast haste. Do things.

Turn 2: Cast invisibility (end haste). Be invisible. No movement, no actions.

Turn 3: Be invisible. No movement, no actions. (Resolve haste)


The section on “Concentration” states:

[…] You lose Concentration on a spell if you cast another spell that requires Concentration. You can’t concentrate on two Spells at once. […]

The haste spell states:

Casting Time: 1 action […]

Duration: Up to 1 minute […]

When the spell ends, the target can’t move or take actions until after its next turn, as a wave of lethargy sweeps over it.

The invisibility spell states:

Casting Time: 1 action […]

Duration: Up to 1 hour […]

The spell ends for a target that attacks or casts a spell. […]

Haste spell: what does “one weapon attack only” mean?

While making a Bladesinger Wizard, I wondered if I would be able to use Booming Blade twice while hasted.

Booming Blade: As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell’s range, otherwise the spell fails.

Haste: Until the spell ends, the target’s speed is doubled, it gains a +2 bonus to AC, it has advantage on Dexterity saving throws, and it gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

What exactly does “one weapon attack only” mean? Is this to prevent characters with the Extra Attack feature from making 2 attacks? Does this prevent me from casting 2 spells (cantrips or higher-level spells) in a single turn?

If a creature with Multiattack is affected by Haste, can it make two Multiattacks?

It’s a fairly straightforward question.

A creature has a Multiattack option, and it also can cast the Haste spell. While under the effect of Haste, can it use the second Action to take another Multiattack Action?

My main concern is the clause of the Haste spell that limits the number of attacks made from taking the Attack Action. This is a different Action, though.

Then there is the concern of being able to use Multiattack at all, because Haste says what kinds of Actions you can take.

Would it harm game balance to allow the Haste action to be used to drink a potion?

RAW, Haste specifies:

[The target] gains an additional action on each of its turns. That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

And it has already been stablished that “Use an object” is not valid to use a magic item which to my understanding includes drinking a potion.

So my question is, would it break balance much to actually disregard that and allow the drinking of a potion as one of the actions granted by Haste?

Does haste extra attack gets triggered when you cast haste on yourself?

My question here is what is the right combination of the answers from these two questions:

  • Does Extra attack stack with haste?
  • Can you get an extra attack after casting a spell whilst hasted?

Assuming I’m a level 5 fighter / level 5 wizard and I cast haste on myself.

It’s clear from the second question I can then proceed to use the attack action as per haste. My interpretation:

  • RAW is you get only one attack and extra attack does not get triggered as per the answer to the first question.

RAI it looks like that particular line “one weapon attack only” was intended to limit attack explosion on the fighter:

The “one attack only” stipulation is preventing the use of the extra attack feature in the additional action, so a character with extra attack could use his regular action to make 2 attacks and use the additional action granted by haste to attack once more. This is to prevent say, a fighter at level 20 who gets 3 extra attacks from having 8 attacks in a single turn on top of a possible bonus action.

As specified in the answer of this other question.

Is there any indication (by WOG or similar in either direction) as to where in this particular scenario the fighter would get the extra attack? Which would mean, if you cast haste on yourself on your turn, the effect of casting haste is you get to do your turn as normally without the benefit of haste but also without having lost the action into casting haste.

Do you get the extra attack from a Haste spell you cast on yourself with 1 round duration?

A rogue PC in my campaign has just picked up the Trapsmith prestige class and gained spellcasting this way. He picked Haste as one of his first spells. Now I wonder: His current caster level is 1. If he casts haste, how long does it last? Only the round he casts the spell? Then he would only benefit from increased speed (+30 feet or double, whichever is lower) and +1 dodge to Reflex and AC until his next turn. Or could he transfer the benefit to the next round, if he takes his move action first and then casts the spell with the standard action?