Some planar shepherd questions won't generate good answers when the questions are about the class's abilities' interactions with planes outside the Eberron campaign setting. That means, as always,
Ask the DM
The Wilderness of the Beastlands has never received the attention the higher profile planes receive. Like the previous question about the Outlands, the planar shepherd who picks a fictionally underdeveloped plane1 with which to link is at no particular advantage over a planar shepherd who picks a fictionally well-developed plane.2 A planar shepherd who picks an unpopular plane just leaves more of his options up to the DM.
The Beastlands' Magical Beasts
There's just one.
In addition, native to the Beastlands is the beast dragon (Dragon #321 50-1), a dragon with the extraplanar subtype, and the dread blossom swarm (MM3 45), a plant. No single template changes dragons or plants to magical beasts, however.
Template Shenanigans
There's no template that makes an animal into a magical beast by making it more beastlandish, but that's okay because the Beastlands specifically calls out the template celestial, which "can be added to any corporeal animal, aberration, animal, dragon, fey, giant, humanoid, magical beast, monstrous humanoid, plant, or vermin of good or neutral alignment" (MM 31), so that template's pretty wide-ranging.
And while it's interesting that the Beastlands "is the home of many beasts of legend--superior versions of powerful animals, beasts, and magical beasts" (MP 142), that doesn't let the Beastlands-attuned planar shepherd break the rules of the template monster of legend, which says that it "can be added to any animal, beast, magical beast, or monstrous humanoid .... The creature’s type changes to outsider [not magical beast], though the monster of legend’s home plane is the Material Plane" (MM2 213), not the Beastlands. So what, exactly, that sentence means is up to the DM; perhaps the DM'd be willing to homebrew some creatures, convert some from a previous edition, or allow 3rd-party sources to satisfy this note.
But ask the DM if the planar shepherd's level 3 wild shape special ability that permits him "to change into a magical beast native to [the] chosen plane" and "includes creatures whose type changes to magical beast as the result of applying a template" (FE 106) also includes templates other than the examples celestial or fiendish. If yes, there are templates that can be added to animals to change their types to magical beasts. In my opinion, those appropriate for Beastlands animals include the following:
- chimeric creature (MM2 206).
- kaiju (Dragon #289 68-71). Note: Using wild shape to assume the form of one, though, is quite the challenge.
- monstrous beast (SS 122).
- valicorn ("Ghostwalk Web Enhancement" 4-5).
- winged creature (SS 137).
Any of these could satisfy the "beasts of legend" flavor text of the Beastlands.
The Beastlands' Native Outsiders
In Dungeons and Dragons, 3rd Edition the following outsiders are native to the Beastlands:
Some neutral good angels. According to the Monster Manual, one of the sources of "neutral good angels [is]... the Beastlands" (MM 10).
After the Monster Manual Wizards of the Coast published no further angels.
- The hollyphant (BE 176-7).
- The spirit of the wild (Dungeon #148 25)
- The xap-yaup energon (PlH 122).
Unlike many planes, the Beastlands never received their iconic creatures--the plane's popularity never even spawned a race as sparsely detailed as the rilmani from the Outlands or the demodands of Carceri. The closest I could find from earlier editions are the mortai, converted to Dungeons and Dragons, 3rd Edition here, and, honestly, I don't think they count.
live in Remains Different from native to
It's obvious you want the answer to be different, but Jack Lesnie's correct when he says that these terms mean different things. Seriously.
- "Lawful good angels hail from the plane of Celestia, neutral good angels from the plane of Elysium or the Beastlands, and chaotic good angels from plane of Arborea" (MM 10).
- "Archons are celestials from the plane of Celestia" (MM 10).
- "The eladrins are a celestial race native to the plane of Arborea" (MM 93).
- "Guardinals are a celestial race native to the plane of Elysium" (MM 141).
- "Lillends are mysterious visitors from the plane of Ysgard" (MM 168).
...And so on. An outsider's entry tells the reader what plane a creature's native to. All the other times when a creature is mentioned as hanging out on another plane, such a creature can only live in another plane. He's not native to it.
- While I find researching these questions interesting, there just isn't that much information about Arborea, Bytopia, Ysgard, Pandemonium, Carceri, and the like.
- In fact, short of the Abyss, Celestia, Baator, Limbo, and Mechanus, not a lot's been said about many planes.
Any answer (and thus any successful argument on your part) is dependent upon the ecology of the world as your DM envisions it. Per PHB page 65, a Druid is all about the ecology of the world, its balance, and against that which is unnatural, which includes aberrations.
The General Differences
Some of what makes any aberration or monstrosity "cooler" (your words) is the unnatural (be it demonic, alien, magical, etc) innate ability inherent in the creature. I'll offer two examples:
Monstrosity (Cockatrice, MM p. 42, CR 1/2) has the ability to turn things into stone. That is a powerful special effect. No
beast has one similar at that level. (See conditions: Petrify,
restrained, PHB 291). Compare to a CR 1/2 Ape (MM page 317). He can
make two fist attacks, but he can't turn you to stone.
Aberration (Gibbering Mouther, CR 2, MM p. 157) has the gibbering effect much like the Confusion spell, a fourth level spell. (PHB: p. 224) A Cave Bear is a beast of CR 2 with a non-trivial damage output (1d8 + 2d6 + 10) but no magical effect. A Giant Constrictor Snake does 2d8 +4 and may restrain a creature (lock it down), which is hard on a single creature. Confusion (a 4th level spell effect) at will is far more powerful and can have an impact on multiple creatures.
The examples are not exhaustive. Another example1 would be a monster that is invulnerable when it does not attack - this would be annoying on a monster, but on a PC it could significantly unbalance a campaign. (1 @NeilSlater pointed this out in a note).
An argument against this proposal is that beasts don't have special abilities as powerful as aberrations or monstrosities at similar CR levels.
Another argument against Aberrations is the specific enmity Druids have against such unnatural creatures.
An argument for this proposal is that some beasts do have magical abilities. See Flying Snake for example. (MM p. 322) Flying snake: real snakes don't fly; fly is a third level spell.
RAW
Monster Manual on Aberrations, Beasts and Monstrosities
Aberrations have innate magical abilities drawn from the
creature's alien mind rather than the mystical forces of the
world. (p. 6)
Monstrosities: Not truly natural, and almost never benign. (p. 7)
Beasts: Natural part of the fantasy ecology. Some have agical powers. (p. 7)
Druids (PHB)
Revere nature above all, and get their powers from nature itself, or a
nature deity. (p. 64)
This is mostly arguments against. Natural is what a Monstrosity or Aberration is not.
But ... your DM may wish to pursue this with you
What does your DM consider to be natural, and a part of the ecology of the world? There are many Beasts in the Monster Manual that take our primary world animals and make them something 'magical' or 'fantastic' or 'unnatural' (pick the term you want to you use), even though they are well placed in your DM's secondary world. If there is a place in his world where Gibbering Mouthers are as common as elk are in ours, you have a stronger case than if there isn't.
If you want to sell the case for going beyond Beasts, I suggest that for the mechanical approach you compare the innate abilities of a similarly CR rated Monstrosities with various Beast's and see how the power stacks up.
Based on my brief review, the Monstrosity or Aberration tends to have a more powerful effects per CR. Perhaps, for Monstrosities, agree to a CR divided by two or CR divided by four, or a CR one to two steps down CR table2 as compared to Beast of similar CR that your Druid can transform into. (2Tables on page 112, Basic rules). Aberrations would be a harder sell in any case, even with a power reduction.
You may find a way to make it fit if the DM waives the RP element of what Druids are in the general context of D&D as applied to the specific ecology of the DM's world. You could argue that a Winter Wolf is a highly evolved wolf species that was influenced by the Weave (or magic as a native feature of a magical world) and could fit as Beast versus Monstrosity in terms of category (mechanics). This would still require balancing of special abilities.
For purposes of this discussion, I'll treat the table in the PHB as capping CR at 1 (Druid Level 8) for Wild Shape. This avoids the need to compare your Druid's related at will power (cantrip frostbite, 1d6 dmg to one target (Elemental Evil supplement, p. 18; also XGtE)) with cold breath (dmg 4d8 15' cone, recharge on 5-6). How would you scale down a spell which is between 3rd or 4th level in power to fit your Druid's at will power, and fit within the limits on spell casting in Wild Shape? Cold Breath is between Snilloc's Snowball Storm(2)(dmg 3d6, 5' sphere)and Cone of Cold(5)(dmg 8d8, 60' cone). As @Miniman points out in his answer, you can see how fast these at will abilities can get overpowered.
The Balance Problem
We'll look at Worg and Death Dog (Monstrosities) (Canine examples because I love my dogs. :) )
CR 1/2 Worg (1 melee attack, 2d6 +3)
- Two added languages (Goblin and Worg) which could make for some
interesting interaction and infiltration scenarios.
- Advantage for rolls based on your wisdom on smell and hearing Perception checks.
- "Knock prone" ability in combat (con save DC 12 or target falls prone).
Compare that to CR 1/2:
Ape: two fist attacks, each at 1d6 +3. Passive perception will be
overwritten by your WIS and Proficiency.
Black Bear has two attacks, bite and claw, 1d6 +2 and 2d4 +2
respectively. Advantage on smell Perception checks. (WIS).
Worg might be sellable, but it has more advantages than other CR 1/2 beasts. Does the DM require a level minimum above 4 (5? 6? 8?) to Wild Shape into one? Would he apply CR/2, and make you wait for 8th level to try that form? Another point: maybe you have to encounter and defeat a Worg, not just have seen one, to take on the shape.
Caution: the Cockatrice example returns for CR 1/2 finds a creature who inflicts on a non-saving target a Hold Person with no need to maintain concentration. That's more than a 2d level spell effect, more like 3rd or 4th. A free spell applied how many times in a given combat and not on the list of prepared spells? Big power boost. At level 4 Druid, you don't have any 3rd level spells.
CR 1 Death Dog:
- Two bite attacks per round (1d6 +2 each).
- Advantage on all Perception checks.
- Advantage on saves versus: charm, blinded, deafened, stunned, frightened, knocked unconscious.
The bite contains the balance breaker. If not saved against (CON DC 12) it creates the poisoned condition (Basic rules, p. 172) and causes a disease.
If the target is a creature, it must succeed on a DC 12 Constitution saving throw against disease or become poisoned until the disease is cured. Every 24 hours that elapse, the creature must repeat the saving throw, reducing its hit point maximum by 5 (1d10) on a failure. This reduction lasts until the disease is cured. The creature dies if the disease reduces its hit point maximum to 0. (Basic Rules, p. 123)
Poisoned
• A poisoned creature has disadvantage on attack rolls and ability checks.
A successful melee hit creates a spell-like effect which (if there is no save) drains max hit points (1d10) from the target. This is twice per round, one per attack. The impact of this increases with the number of opponents. During a single encounter, the disease may not be that big of a deal, but during the battle the poisoned condition imposes a significant problem: disadvantage.
Death Dog is a tougher sell than Worg. (At Druid level 8, you have 4 cantrips, 3 3rd level spells and 2 4th level spells).
Could the overboost for Death Dog be balanced? Maybe. Maybe each time your bite triggers that save requirement, your DM has you burn a spell slot (second level?) That might get closer to the balance. (Hey, wait, I thought Druids were all about the balance! :-) ) A problem is that this extra work gets the game (and the other players) away from how spells usually work in D&D 5th edition.
Brown Bear. CR 1.
- Two attacks. 1d8 + 4 and 2d6 +4, bite and claw.
- Smell Perception check boost (Wis).
- No imposed condition, no free spell/spell effects. No long term effects.
These two don't compare as well as my cherry-picked examples at CR 1/2.
So much for a rough illustration of the balance problem. It is a chore for your DM and you. If you both want to put in the work, you may arrive at something usable. This might be a step beyond how far the DM is willing to go to homebrew.
Is this a challenge to the Druid Class trope? Yes. Were I the DM, I'd say "No" due to how I see Druids in the scheme of things, but I'm not your DM. Each DM has his/her own world, so you may have some room to brew.
Best Answer
Even with the restriction you propose, there are potential balance problems. Your DM will have to agree on any list of approved additions to Beasts, as well as a way to scale down the at will powers (super cantrips?) a given Monstrosity or Aberration has. Before I get into analysis:
A step in the right direction. You still have spells, at will, at levels of varying power.
Some at will abilities are very powerful. I'll offer one example with your Int restriction included to illustrate. I suggest you do a similar analysis for each candidate creature you identify and propose it to the DM, with any suggestions for power mitigations for at will abilities.
Basilisk
Other beasts do decent damage and poison. (CR 3 Giant Scorpion, for example).
Your INT, CHA, and WIS carry over, so you don't pay the penalty on saves or ability checks that an ordinary basilisk has. (OK, a basilisk is hardly ordinary ... ) Carry over is a feature of Wild Shape.
If human, free darkvision at no spell cost. Some beasts see-in-the dark, no problem.
(Basilisks were never much for small talk). :-)
The at will ability that needs work.
Petrifying Gaze.
This is an at will ability (like a cantrip) in the form of a spell effect that is at least 3rd level, per the cockatrice in the other question. At least as powerful as Hold Person with no need to concentrate, except that the DC is lower than a spell that you'd cast with your WIS bonus as a Druid.
Note that this isn't an Action: it's like an aura. (Or maybe a bonus action?). It's like having a wand or staff of this ability with dozens of charges. Magical items are scarce in 5e, and here you can turn into this thing and get a wand's worth of stuff ... and don't need an Action to make the magic work! Power a-plenty, could need scaling back.
Just standing around, for the duration of your transformation, you can expend an equivalent of most of your spell levels in power, maybe more, with this feature alone. This with a creature you can become as a 9th level CoTM Druid.
While it takes 2 failed saves to turn to stone, a statue is out of the fight for good. (More on that later). If one of your party casts Bane and some saves are at Disadvantage you could make multiple statues with some haste. Fight's over. It takes a fifth level restoration spell per creature to undo this change in status. (On the other hand, your garden decoration needs would be solved, so that's a plus).
In terms of Encounter Balance: you spend no spell slots and require of your enemy the cost of a fifth level spell to get back into the fight.
My DM has us attack at disadvantage if we avert our eyes during combat to avoid things like an Umber Hulk's gaze/Confusion. (Related to RAW on targets you can't see ...) Against this Basalisk-Druid, foes at melee and short-spell-or-missile range will have disadvantage just because you are there. No need to cast any sort of spell (like the Cleric's Bane) to inflict it upon them. No need to poison them and have them save versus poisoned condition. (They may already be doing that against your bite!)
Encounter Balance problem number 2: you get free 1st-or-2d second level spell effect slots for as long as the fight lasts but spend no spells.
How many CR3 beasts have that edge in a fight?
How do you scale down the flesh-to-stone super-cantrip that operates in an area of effect (3d / 4th level power)? Let's look at some cantrip level powers, Wizard:
Acid Splash, Fire Bolt, Mage Hand, Minor Illusion, Poison Spray, Ray of Frost, Shocking Grasp
If you can nerf the gaze into that power range, or a lower level spell, this might fit a bit better in the case for a Monstrosity.
Huzzah, a weakness for the DM to exploit! You'll run into an enemy fighter with a shield that is polished to a mirror finish! :-) (Perseus' Shield from Greek mythology, versus Medusa).
Second order effect and a nasty bonus power. You can turn your enemies to stone, eat them, and then head to the latrine to dispose of them. This isn't quite as powerful as Disintegrate spell, but it's up there. How many fourth and fifth level spells per day does a Druid get at 9th level? At 11th level? At 15th level?
Idea: Scale down the gaze to a bonus action between "Ray of Frost" to a mini "Cone of Frost" power levels, an effect that slows down your foe, maybe multiple within (___) range. You already get free disadvantage with your gaze. Its' still a free spell, and a spell you didn't have to choose or prepare, in terms of equivalence. (Oh, and you aren't really playing a basilisk anymore). Between you and your DM to work out the particulars.
A similar sort of analysis should be done on a per-creature basis to get the balance into the ball park. Work with your DM.