Best base class for a homebrew subclass inspired by Doric from the movie?

Question

A lot of D&D fans have noted that, unlike how Doric’s Wild Shape is presented in Dungeons & Dragons: Honor Among Thieves, D&D druids have almost never had the ability to transform into owlbears, certainly not in the latest edition of the rules. There are a number of other discrepancies, like the fact that she can switch from one form to another without stopping in her regular tiefling form, and also that she is not a spellcaster and

cannot attune the helm of disjunction.

Obviously, the movie wasn’t really following the rules anyway (the slowly-expanding time stop isn’t a thing, I don’t know what that thing on Simon’s hip was, etc.), so no critique of the movie—but it did get me thinking.

Prior to the movie, we had a question about balancing a druid turning into an owlbear and the like, but now that I’ve seen it, I’m fairly sure—despite the fact that she was called a “druid” in the movie—the druid class isn’t the best fit for Doric. One can imagine a druid circle like Circle of the Moon but that allows owlbears, perhaps instead of elementals, as suggested in the top answer to that question, but that doesn’t really capture the character that Doric is in the film.

So what I’m imagining instead is a subclass for some other class, that says you learn Druidic and count as a druid socially, and gives you a version of Wild Shape perhaps even better than Circle of the Moon’s (allowing creatures like owlbears, allowing multiple repeated shifts in quick succession, etc.)—but on a class without spellcasting. There’s precedent in D&D for that, in the master of many forms from the Complete Adventurer supplement for the “v.3.5 revised edition” of D&D (though even that, oddly enough, couldn’t turn into an owlbear).

The question is, where to put it? It has to be a class that has fairly-powerful subclasses, and that doesn’t have spellcasting. I’m leaning towards Monk, just because of the shared Wisdom focus and because the subclass could allow Martial Arts to apply to claws and the like. But I’m not super-familiar with 5e, particularly on a meta level like this where you are finding the right platform for this concept, so I’m interested in the expert opinion of this site on the subject. A good answer will not just offer a suggestion, but back it up with analysis of how these ideas fit into the base class and how they would compare with existing subclasses for that class. A sketch of what the subclass would look like seems like a good idea, though obviously this isn’t the place for fully developing (and playtesting) the subclass here.

Answer 1

The Path of the Beast Barbarian is already pretty close to what you're looking for.

Having played a Path of the Beast barbarian, and reading through what you're looking for, I'm comfortable suggesting a Path of the Beast Barbarian, with thematic reflavoring to fit your desired theme. Flavor wise, it's pretty close:

Barbarians who walk the Path of the Beast draw their rage from a bestial spark burning within their souls. That beast bursts forth in the throes of rage, physically transforming the barbarian.

Such a barbarian might be inhabited by a primal spirit or be descended from shape-shifters.

For features, you've got the generic barbarian suite, and the 3rd level feature, which serves as the foundation of the rest, looks quite a bit like the Wild Shape style feature you're after:

When you enter your rage, you can transform, revealing the bestial power within you. Until the rage ends, you manifest a natural weapon. It counts as a simple melee weapon for you, and you add your Strength modifier to the attack and damage rolls when you attack with it, as normal.

The 6th level feature expands your utility, giving you a choice of improving your Climbing, Jumping, or Swimming abilities while in your beast form.

The base Barbarian is a suitable scaffolding for your subclass.

Where Path of the Beast and Rage are notably lacking is duration. Wild Shape lasts a number of hours equal to half your druid level. Rage lasts one minute. But you asked for a class to serve as the scaffolding for a new subclass: barbarian is it. The base barbarian features are already on theme for a hard hitting, martial-focused druid-like character, with features like Unarmored Defense, Feral Instinct, and Danger Sense. With Rage being the Barbarians primary gimmick, I think it's a great candidate for wholesale replacement with a more robust Wild Shape-like feature than the one found in the Path of the Beast. One advantage here is that the features' action and resource economies are pretty similar. Rage and Wild Shape are both bonus actions, and Wild Shape is "twice per short rest", while Rage is 2-6 times per long rest, scaling up with level.

Overall, I think substituting Wild Shape in place of Rage will be a pretty even trade. Many of the base barbarian features interact with Rage in some way, and would just need to be tweaked to interact with the new Wild Shape feature.

Answer 2

Barbarian

There are not that many options for non-casters, namely the Barbarian, Fighter, Monk, and Rogue.

While the Monk fits this criterion, and is thematically appropriate, it doesn't fit your second criterion: powerful subclasses.

For the Barbarian, the subclasses offer comparably powerful bonuses, but mostly when entering rage or while raging. Attaching an Owlbear transformation to rage seems practical because an unrestricted ability to transform is probably too powerful.

Importantly, the subclass Path of the Beast is already very close thematically to what you are trying to do.

Answer 3

Warlock

Invent a patron especially interested in wildness, beast forms, changing shape, the eternal truth that is constant change, and physical battle.

Although not strictly speaking a class without spellcasting, this could be played as a warlock that primarily casts spells on themselves for the purpose of powering their unarmed (and eventually transforming) melee combat.

Your Spellcasting Ability is Constitution, not Charisma.

Savage Mark
Starting at 1st level, you gain the ability to cast Hunter's Mark as a bonus action and without spending a spell slot. The extra damage triggers only from damage you do in melee. You can’t use this feature again until you finish a short or long rest.

Wild Warrior
At first level, you gain proficiency with medium armor. Whenever you make an unarmed strike with one hand, you may make an unarmed strike with your other hand as a bonus action. Your unarmed strike uses a d4 for damage.

Pact Boon
At 3rd level, your otherworldly patron bestows a gift upon you for your loyal service. You may cast alter self as a bonus action and without using a spell slot. You can’t use this feature again until you finish a short or long rest.

Whenever you return to your true form from another form, you may spend HD to recover hp as if you had taken a short rest.

6th Level
You may cast spells when you are not in your true form, even if your current form does not have Spellcasting, provided those spells target only yourself. These spells may be cast without any components except ones which are consumed by the casting.

RAW Sculptor of Flesh Invocation:
Prerequisite: 7th level

You can cast polymorph once using a warlock spell slot. You can't do so again until you finish a long rest.

With this patron, when you select Sculptor of Flesh, your accessible forms include Monstrosities as well as Beasts. Monstrosities count as 2CR higher than their stat block indicates for the purpose of your transformation.

10th level
While in another form that is not your true form, you are resistant to bludgeoning, slashing, and piercing damage from non-magical weapons. In your true form, you are resistant to poison and psychic damage.

14th level
If you possess the Sculptor of Flesh Invocation, the limit to the number of casts per long rest is lifted, although you must still expend a warlock spell slot to do so. In addition, on a short rest, you regain any spell slots you used to cast polymorph, on yourself only, since your last rest (long or short).

By 14th level you have someone that can polymorph themselves three times per short rest, into beast forms up to CR14 or monstrosities up to CR12, and can transform from one form into another without having to return to their true form.