What would be broken if I let my druid player turn into any creature of appropriate CR?

What would be broken if I let my druid player turn into any creature of appropriate CR?

what system?

On one hand yes, on the other hand, he's a druid and probably already broken anyway.

Remove his other spellcasting abilities and make his saves/defenses closer to that of a Wizard.

Boom, just fixed the druid.

If we're talking 5e, the REAL fix the druid needs is not being able to get a new HP bar every time they transform and effectively the amount of damage they can soak up multiplied by the number of transformations they have each day.

If 3.5 or Pathfinder, don't fucking do that.
Druids are strong enough, read the goddamn rules and don't give them huge boosts they don't need.

It's not different from barbarian raging or just having high AC; all of those are effective HP multipliers.

The problem is only that the druid gets to do it all the fucking time (after level 18, literally), when it's a better version of the barbarian's rage.

Rage adds a small amount of temporary HP to a Barbarian's HP and comes with penalties when the rage ends (until really high level).

Wildshape literally gives the druid an entirely new HP bar on top of their existing one and comes with no penalties at all when it wears off, where it can be then be used again to give the druid a new HP bar before they even take any damage in their human form.

Short of Save or Die effects or massive damage that can bleed through two entire HP bars at once, a druid is basically invincible as long as they have transformations left, because transforming essentially gives them a full HP bar for free.

Nothing that isn't broken already.

>Rage adds a small amount of temporary HP to a Barbarian's HP and comes with penalties when the rage ends (until really high level).

Excuse me, I though we were discussing 5e.

Barbarians don't get any HP for raging in 5e, at all.

Arguably their damage resistances can "multiply" their HP, but that only applies to physical damage unless you take a specific totem path. And even then it doesn't do anything to mitigate damage you've already taken.

A thousand times this.

The things is that "beasts" have more or less mundane abilities, and no language / low int. A few can fly (but you can't wildshape into those before pretty high lvl) - some have poison or multi-attacks, or similar.
Beasts, pr. definition, don't do magic shit.

If you allow the player to wildshape into "monstrosities" or "fey creatures" or "magical beasts" you are suddenly stuck with an endless array of highly exploitable abilities.
Say - wildshape into pixie, gain polymorp. Wildshape into a myconid sovereign (CR 2) and gain the ability to make fungal zombies that last 24 hours.
For straight melee, always wildshape into an Ogre, (CR 2).
For stealth-shit, always wildshape into a Will'O wisp and have the ability to move through walls and objects, while being invisible.

It is essentially gonna let your player be the best at everything the party will try, and rob other players of chances to shine with their abilities.

Mind you, some Magical Beasts really don't deserve the title. Like Razor Boars. It's a boar with sharp tusks, literally no supernatural or spell like abilities.

>For stealth-shit, always wildshape into a Will'O wisp and have the ability to move through walls and objects, while being invisible.

Fuck, as far as stealth goes, even the ability to turn into something as mundane as a cat is super great for stealth. Nobody ever suspects the stray alley cat of spying on them, unless they have some sort of magical-detecting countermeasures to tip them off to your transformation.

Druids are one of the most mechanically problematic classes in the game, especially at low levels Thankfully they're so boring nobody ever wants to play them.

That is true. And it would be a cool gimmick to let a druid branch out a little, if it was fluff-appropriate.
Like, he could also become a Razor Boar, and a Displacer Beast, and stuff.
But just saying "any creature with appropriate CR" opens the door to a great deal of fuckery.
As "circle of the moon" Druid you can basically go for CR1-creatures from lvl. 2-6, and CR2-creatures from lvl. 6-9.
This ability would be wildly unbalanced, even at lvl. 9, compared to the power-level of the rest of the party.

Making it CR at all is kinda a bad decision.

I preferred the 4e way of doing it where it was more a template for the PC with (Scaling with you) powers for wild shaped stuff. Rather than 'Sorry wolf-themed druid. There are no good wolves for X levels' or 'Sorry bear-themed druid you have to start off with wolves'

You are thinking of irl. A real cat, in the real world, would be amazing at stealthing.
A D&D 5e cat has a flat +4 to stealth-checks, and 2 hp.

Meanwhile, a will' o wisp can fly, is incorporeal, and can cast invisibility at will.

Actually, I'm an idiot. Sorry, reading comprehension of a 4-year-old. I was thinking of stealth mechanics. You are obviously right that a guard would have no reason to suspect a cat was in fact a sneaky druid.

1) CR is a busted system
2) Even IF it worked right, a monster of CR X is equivalent to a WHOLE PARTY of X level.
3) With Natural Casting he'll have his own spells on top of the monster.

So in short: shit gets broken very much.

As a newbie to 5e, is Circle of the Land ever worth taking? Or is it strictly inferior to Circle of the Moon archetypes?

>2) Even IF it worked right, a monster of CR X is equivalent to a WHOLE PARTY of X level.
This has never been the case. An equivalent CR fight is supposed to be a reasonable fight for the party - meaning the party is supposed to WIN against it. A boss fight, where there is supposed to be actually a reasonable chance of the PCs losing, is going to use either higher CR monster or multiple monsters.

I fix it by giving the druid a level of exaustion after each transformation back into human. If they lose all hitpoints in animal form and are forced to revert, damage overflow hits their hp, and they instead suffer TWO levels of exhaustion.

That would be true, if [1] wasn't aq thing. Refer to the basest broken monster in 3.5, the Hydra. Now to the Pyro/Cryo versions. Now go looking for the other MM books. That's the point.

I fucking hate druids for this. It makes it so much harder to correctly balance encounters. That, and their spells that magically generate food and drink and ruin survival immersion.

Circle of the Land is arguably more flexible. If you're just looking to minmax, take that. If you're looking for fun, go Moon.