How Do “Random Attack” Effects Work Against Characters With Multiple Attacks?

I have a party of 13th level characters, one of which happens to be a fighter who loves to swing her dual hammers at anything within reach. Recently I’ve been experimenting with some custom monsters and they are going to encounter a Gibbering Mouther/Minotaur hybrid, but before they get there I want to clear up a question I had. Gibbering Mouthers have an ability called gibbering, which reads as follows:

The mouther babbles incoherently while it can see any creature and isn’t incapacitated. Each creature that starts its turn within 20 feet of the mouther and can hear the gibbering must succeed on a DC 15 Wisdom saving throw. On a failure, the creature can’t take reactions until the start of its next turn and rolls a d8 to determine what it does its turn. On a 1 to 4, the creature does nothing. On a 5 or 6, the creature takes no action or bonus action and uses all its movement to move in a randomly determined direction. On a 7 or 8, the creature makes a melee attack against a randomly determined creature within its reach or does nothing if it can’t make such an attack.

The part I was particularly interested in was the last part, where a creature who rolls a 7 or 8 makes a melee attack against a random creature within range. Given that the fighter has 3-4 attacks normally, not including her action surge which can effectively double that, how many attacks should she be randomly making? Is she effectively using the full extent of her attack action to swing wildly, or would she only make the 1 attack and call it quits?

How do you choose active effects when two instances of the same spell/feature overlap?

There are two slightly different rules when it comes to overlapping game features, one from the PHB (post-errata) and one from the DMG (post-errata):

PHB:

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don’t combine, however. Instead, the most potent effect – such as the highest bonus – from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

DMG:

Different game features can affect a target at the same time. But when two or more game features have the same name, only the effects of one of them—the most potent one—apply while the durations of the effects overlap.

The current answer to my question “Do the Stone Golem's Slow feature and the Slow spell combine?” states the following:

[…] Backed by the PHB’s mention of effect-based potency, I compare each individual effect two features of the same name have and then pick the strongest for each. That also constitutes that the unique parts of one feature are compared against “nothing”, meaning by virtue of existing they’d trump the lack of any counterpart in their twin […]

And goes on to apply this method to blindness/deafness allowing both effects to persist simultaneously in direct contrast to the current answer to the following: “If you cast Blindness/Deafness on the same creature twice, what conditions are applied?”

Which method of comparing two features is correct:

  1. One feature/spell is determined to be “more potent” and all effects of the other feature/spell are ignored.

  2. The effects are compared one-by-one, thus different parts of each feature/spell can be active at once.

How many rings that have special effects can one character wear at a time while still having all of the special effects [duplicate]

This question already has an answer here:

  • Is there a limit to the number of magic rings a character can wear on one hand? 3 answers

So i was wondering how many magical rings can one character wear at once while still retaining their special effects.

Advantage against spells and magical effects equating to damage resistance?

So my DM said that monsters that have advantage against spells and magical effects are extra resistant to damage? We fought some demons, it has resistance to slashing, piercing, and bludgeoning damage from non-magical attacks, we all have magical weapons but he was saying that the monsters were still resistant to the damage because they have advantage against magical effects?

Can a Hunter Ranger under the effects of the Shapechange spell use Whirlwind Attack with a Monster’s attack?

The Hunter Ranger’s Whirlwind Attack feature states:

You can use your action to make a melee attack against any number of creatures within 5 feet of you, with a separate attack roll for each target.

I’m wondering whether you could use the shapechange spell in conjunction with this feature, the spell states:

[…] You retain the benefit of any features from your class, race, or other source and can use them, provided that your new form is physically capable of doing so […]

Does this mean that a Ranger who is transformed into, say, a Bulette could use their Bite attack with Whirlwind Attack?

What can a character do under the effects of a feeblemind spell based off the INT of 1?

I’ve been going through the posts on feeblemind, but haven’t found one that explains, other than what is specifically mentioned in the spell, exactly what can be done while under it’s effects.

It is clear that a creature can’t cast spells, activate magical items, understand language, or communicate. It is also clear that they can identify friends, follow them and “protect” them. The spell does not specify any other effects, but…

The spell drops the character’s INT and CHR to 1. This leaves a character with the intellect of a bug or lizard. The one thing the spell does not go into detail over is what that means for the character.

Is there anything RAW that indicates what a character/creature with an INT of 1 can actually accomplish?

In my mind, any character would be able to avoid attacking friends (it says so), but when given multiple baddies, would the player be able to specify which baddie they attacked (with the player choosing the most opportune target obviously)? Or would a random roll be appropriate? Or, if already attacked by a baddie, would it be appropriate to tell the player “you are fixated on this creature, since it hurt you?”

What about proficiencies with weapons? To me, an INT of 1 means they can’t recall how to use tools/weapons, as this is based on memory. that wouldn’t necessarily preclude the use of them, but it would remove the prof. bonus.

As for character abilities, I don’t think an INT of 1 would necessarily preclude their use. I do think it would be situational, based on the ability.

Am I reading too much into this? Is this all in the domain of “It’s the DM’s call?” Should I stick with “the spell doesn’t specifically forbid it, so it’s good to go?”

What is the cheapest way to damage myself and trigger the effects of the Fade Away feat?

For clarity, I mean cheap in the sense of the action economy. The ideal scenario would be to damage myself with a free object interaction or a small amount of movement.

Here is the relevant text of the Feat:

Immediately after you take damage, you can use a reaction to magically become invisible until the end of your next turn or until you attack, deal damage, or force someone to make a saving throw. Once you use this ability, you can’t do so again until you finish a short or long rest.