So my question is, does the manifestation count as an unarmed attack?

By that I mean, let's say I take a dip into Monk for the martial arts feature, can I make the attack as a bonus action unarmed attack?

"When you use the Attack action with an unarmed strike or a monk weapon on your turn, you can make one unarmed strike as a bonus action. For example, if you take the Attack action and attack with a quarterstaff, you can also make an unarmed strike as a bonus action, assuming you haven’t already taken a bonus action this turn."

So I take any of the natural manifestations, like the tail, can I make 2 attacks with the Attack action and another attack as a bonus action with the tail again at LVL 6? Or do I only make the 2 tail attack and then a d4 as a bonus action? Or none at all?

Form of the Beast

3rd-level Path of the Beast feature

When you enter your rage, you can transform, revealing the bestial power within you. Until your rage ends, you manifest a natural melee weapon, choosing one of the following options each time you rage:

• Bite Your mouth transforms into a bestial snout or great mandibles (your choice). Your bite deals 1d8 piercing damage on a hit. Once on each of your turns when you damage a creature with your bite, you regain a number of hit points equal to your Constitution modifier (minimum of 1 hit point).

• Claws Your hands transform into claws, which deal 1d6 slashing damage on a hit. When you take the Attack action on your turn and make an attack with your claws, you can make one additional attack using your claws as part of the same action.

• Tail You grow a lashing, spiny tail, which deals 1d12 piercing damage on a hit and has the reach property.

You manifest a natural melee weapon, it is not unarmed attack. But jeremy crawford did said that claw attack is exceptional, they did consider as unarmed attack. So that mean, if you take anything else other than claws, you cannot use it as unarmed attack.

https://twitter.com/jeremyecrawford/status/955566965619240960?lang=en

So if I use the claws (which was what I planned anyway XD ) at LVL 6 I can make 4 attacks? Using my action and bonus I mean. and will the claws still gain the d6+str+rage damage?

Martial Arts

Your practice of martial arts gives you mastery of combat styles that use unarmed strikes and monk weapons, which are shortswords and any simple melee weapons that don't have the two-handed or heavy property.

You gain the following benefits while you are unarmed or wielding only monk weapons and you aren't wearing armor or wielding a shield.

• You can use Dexterity instead of Strength for the attack and damage rolls of your unarmed strikes and monk weapons.
• You can roll a d4 in place of the normal damage of your unarmed strike or monk weapon. This die changes as you gain monk levels, as shown in the Martial Arts column of the Monk table.
• When you use the Attack action with an unarmed strike or a monk weapon on your turn, you can make one unarmed strike as a bonus action. For example, if you take the Attack action and attack with a quarterstaff, you can also make an unarmed strike as a bonus action, assuming you haven't already taken a bonus action this turn.

Certain monasteries use specialized forms of the monk weapons. For example, you might use a club that is two lengths of wood connected by a short chain (called a nunchaku) or a sickle with a shorter, straighter blade (called a kama).

It did said "you can use Dex instead of Str" and I don't see any wording said "must use dex", so I think there is no issue to using Str. 

Thanks mate XD

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collecting like right now

 Form of the Beast

• Claws Your hands transform into claws, which deal 1d6 slashing damage on a hit. When you take the Attack action on your turn and make an attack with your claws, you can make one additional attack using your claws as part of the same action.

I just read back Form of Beast: Claws, on the second part "When you take the Attack action on your turn and make an attack with your claws, you can make one additional attack using your claws as part of the same action", on level 5 you will gain 3 attack. So that mean you already can launch 4 attack (3 attack from action + 1 attack bonus action) without multiclass to monk. down side is you can't add Str Mod on attack using bonus action.