Does the Doppelganger apply bonus damage from it’s Surpise Attack feature twice?

The Doppelganger gets extra damage if it surprises an enemy and hits it.

Surprise Attack. If the doppelganger surprises a creature and hits it with an attack during the first round of combat, the target takes an extra 10 (3d6) damage from the attack.

Since the Doppelganger gets 2 attack per round, if it hits with both attacks during the first round, will it add the bonus damage on each attack?

How can you detect a Doppelganger?

First, within D&D 5e, what magic, items, or special abilities would allow player characters to detect a doppelgänger?

Second, and perhaps not easily answerable, what types of clues or cue might give away a doppelgänger without the use of magic? Or how as a DM might I give players a chance to notice one?

There is a doppelgänger within the party and I’m struggling to figure out how the players might figure it out. And once they do, how they might track the doppelgänger assuming it escapes.

Thank you.

Are your default racial traits suppressed when choosing the Doppelganger Character Secret?

Icewind Dale: Rime of the Frostmaiden contains a Character Secrets section, one of which is "Doppelganger" :

I’m a shapechanger. I have none of the traits of the race I’m imitating, but I retain my class features, background, and alignment. I have darkvision out to a range of 60 feet. I can use an action to do either of the following at will:

I can innately cast detect thoughts, requiring no components. My spellcasting ability is Intelligence. The spell’s Wisdom save DC is 8 + my proficiency bonus + my Intelligence modifier. I can polymorph into any humanoid I have seen or back into my true form. My statistics, other than my size, don’t change. Any equipment I’m wearing or carrying isn’t transformed. I revert to my true form when I die.

Does this mean that your default race’s traits are nullified when selecting this Character Secret ? Example – a Variant Human Doppelganger wouldn’t have the +1 bonus to two ability scores, the extra skill & extra feat, with that interpretation.

How do you detect a doppelganger?

For plot purposes I replaced an NPC with a doppelganger (one of the advanced “rumored” kind that can steal memories and skills). As this quest progressed, I found that it was actually rather difficult to detect a doppelganger. In this case, he was a cleric in an order of paladins & clerics, so detect magic was out of the question. Supernatural abilities can’t be dispelled. And since the doppelganger had memories and skills (and, for plot purposes, had forgotten he was a doppelganger), a goof up or mistake in “performance” was unlikely. The party got through it and figured it out, but it did have us wondering:

Is there a spell or ability or some obvious racial “tell” that allows players to detect a doppelganger?

Can a doppelgänger regrow a hand?

A doppelgänger does not have the Regeneration special quality. It does have Change Shape (alter self).

Regeneration clearly lets a creature regrow a missing body part, like a hand.

What happens when a doppelgänger in one shape (say, an elf) has a right hand cut off as punishment for stealing, then slinks out of sight and changes shape into a human?

Is the doppelgänger in human form still missing the right hand?

If a hand has to be missing, can the doppelgänger take the form of a human missing its left hand? Hide or disguise the wound to a degree?

How does a Doppelganger monster’s Shapechanger trait differ from the Changeling playable race’s Change Appearance trait?

In D&D Beyond, I compared the Doppelganger monster’s Shapechanger trait to the Changeling playable race’s Change Appearance trait. While I think the two are very similar, some differences stood out. I wanted to see whether my interpretation is correct, since the Changeling’s shapeshifting ability is written less “tightly” than the Doppelganger’s.

The Changeling’s Change Appearance trait says (Wayfinder’s Guide to Eberron, p. 61; emphasis mine):

Change Appearance

As an action you can transform your appearance or revert to your natural form. You can’t duplicate the appearance of a creature you’ve never seen, and you revert to your natural form if you die.

You decide what you look like, including your height, weight, facial features, the sound of your voice, coloration, hair length, sex, and any other distinguishing characteristics. You can make yourself appear as a member of another race, though none of your game statistics change. You also can’t appear as a creature of a different size than you, and your basic shape stays the same. If you’re bipedal, you can’t use this trait to become quadrupedal, for instance. Your clothing and other equipment don’t change in appearance, size, or shape to match your new form […]

What I take from this is that you can take the form of any bipedal creature shaped more or less like the changeling of Medium size (as Changelings are Medium) – so, say, a Mindflayer would be possible, but an Ostrich would not, as the body is too different. A Changeling cannot turn into a Gnome, since they have to remain Medium-sized.

There is no restriction as to the type of creature in the stat block, so any Medium human-structured aberration or monstrosity could be duplicated, as could undead such as mummies or ghouls. The comment on race doesn’t appear to be so restrictive as to mean “You can only change race”, since it says “creature” in multiple places, and not “race”.

In contrast, the Doppelganger’s Shapechanger trait says (Monster Manual, p. 82; emphasis mine):

Shapechanger. The doppelganger can use its action to polymorph into a Small or Medium humanoid it has seen or back into its true form. Its statistics, other than its size, are the same in each form. Any equipment it is wearing or carrying isn’t transformed. It reverts to its true form if it dies.

I take this to mean that it can change into anything humanoid specifically, but can be Small or Medium – so anything from a Goliath to a Gnome in size will work, but not a Mindflayer (whose type is aberration, not humanoid) or a mummy (undead, not humanoid).

A Changeling is more restricted in terms of size, and can only be Medium, but can be any substantially human-shaped creature, regardless of the creature type, while a Doppelganger can turn only into Humanoids, but those must be Small or Medium.

Is my reading of this correct? Or is there some errata or Crawford tweet/Sage Advice that changes this?