How would you build a Shapeshifter as a concept?

[Segev]

Specifically, using the existing classes (core races preferred, though if something stands out to you that is designed as a player race, by all means).

Would you go straight Moon Druid? Straight Transmutationist Wizard? Warlock with the Polymorph invocation (probably not; pretty sure that's a 1/day one)? A mix of Moon Druid and enough Wizard to get to the semi-free polymorph?

If your goal is to spend as little time as possible in your native form (not as a disguise, but actually shapeshifting), what build would you go with, especially to maximize this at low-to-mid level? (Obviously, Moon Druid 20 can do it effortlessly, but that leaves a long time getting there if straight Moon Druid isn't the best way to achieve it at lower levels, too.)

Edit: Assume the DM is not actively hindering this, but isn't going to throw encounters at you to enable it, so "go get bitten by a werecreature" is probably not a viable solution.

This is just hypothetical, but I got curious reading the thread on "what do druids actually do?" as to whether they truly were the masters of this, or if a mixed build would be better.

[Rerem115]

Moon Druid Changeling all the way. You can change several aspects of your appearance at will (more once you get free Alter Self), and can turn into a reasonably sized menagerie of beasts.

If you want to do less but more impactful shapeshifting, Changeling Wizard instead.

[Talij]

Changing or shifter races from the MtG books fit.

Depending on what you want out of the shapeshifting, warlock with mask of many faces might do the trick.

[Grod_The_Giant]

Moon Druid Changeling all the way. You can change several aspects of your appearance at will (more once you get free Alter Self), and can turn into a reasonably sized menagerie of beasts.
Yeah, I don't think there's anything else that comes close. Changeling is the ideal race for some at-will shifting from 1st, and (Moon) Druid is really your only choice for class. Particularly since Polymorph only does beasts, and doubly since Druids learn Polymorph (and Shapechange, eventually). The Transmutation Wizard isn't close.

[Vogie]

"Shapeshifter" is a really broad concept.

Just a member of the Shifter Race, or the Changling race, would fit.

Druids fit, provided your version of a shapeshifter requires them to become an animal specifically.

An interesting Shapeshifter would be a the "Evil Twin" - a Charlatan Whispers Bard with a 2 level dip in Warlock with Keen Mind feat. Whispers Bard for Mantle of Whispers, that allows you to assume the guise of a killed humanoid for 1 hour, including a surge of information. Warlock for Mask of Many Faces, to keep the disguise up for longer. Keen Mind allows you to always remember all the information collected from each person. You spend your waking hours wearing the face of one of your victims.

[Segev]

I was thinking less "Mystique" and more "Beast Boy" when I said "Shapeshifter," though the former is not inappropriate.

Sounds like Moon Druid hits the notes best, since it gets polymorph for non-animal forms and has 2 wild shapes per short rest into as much variety of animal as CR half his level will permit.

Changeling does, indeed, get at least hominid appearance-shifting without costing any other levels in other classes (e.g. 2 of Warlock for Mask of Many Faces). Looking at the racial ability to alter form, I find it amusing it speaks of staying bipedal if you're bipedal and quadrupedal if you're quadrupedal; I don't think anything that would turn them quadrupedal would let them keep the racial altered form ability.

[Tharkun]

@Vogie I really like your concept. I will likely borrow it.