Can a Druid wildshape into a Bestial Spirit form, and if they can, what are the mechanical effects of doing so for the Spirit's stat block?

Question

Summon Beast (Summon Bestial Spirit, freely available UA version of the spell)

Note that I'm linking to the UA because it is freely available and the content for this spell is almost identical to its released version in Tasha's Cauldron of Everything.

This is a question that carries within it many questions.

From the Bestial Spirit Stat block:

Small beast

From the Summon Bestial Spirit spell:

The creature physically resembles an animal of your choice that is native to the chosen environment...

It appears to be both a Beast and a Creature. However, it lacks a CR.

Is there an example of a Beast with no CR?

Yes, DMG Page 169, the Giant Fly (created by the Ebony Fly magic item) stat block lacks a CR entirely.

Wild Shape:

Starting at 2nd level, you can use your action to magically assume the shape of a beast that you have seen before.

Your druid level determines the beasts you can transform into, as shown in the Beast Shapes table. At 2nd level, for example, you can transform into any beast that has a challenge rating of 1/4 or lower that doesn't have a flying or swimming speed.

Would a creature with no CR be considered "less than" the Druid's Wild Shape max CR, or "invalid" for Wild Shape?

If this could be done, given the Bestial Spirit stat block has calculations based on spell level, is there a RAW or RAI way the stat block of the Druid would be determined by?

Answer 1

The lack of a challenge rating makes it an invalid choice.

Wild Shape states:

Your druid level determines the beasts you can transform into, as shown in the Beast Shapes table.

The relevant information from that table is:

Level	Max. CR
2nd	1/4
4th	1/2
8th	1

So at each level we can transform into a beast with CR less than or equal to the CR from the table.

Therefore, to determine if we can transform into the bestial spirit, we ask the question:

Is this bestial spirit a beast with challenge rating {1/4, 1/2, 1} or lower?

It is not, so it is not eligible for Wild Shape. The lack of Challenge Rating is confirmed by the Bestial Spirit's stat block:

Challenge Rating –

There is a discrepancy between DNDBeyond (and the UA version) and the description printed in Tasha's Cauldron.

The DNDBeyond details page and the UA version state in the "At Higher Levels section:

When you cast this spell using a spell slot of 3rd level or higher, the creature assumes the higher level for that casting wherever it uses the spell’s level in its stat block.

The actual printed version of the spell from Tasha's Cauldron of Everything says:

When you cast this spell using a spell slot of 3rd level or higher, use the higher level wherever the spell's level appears in the stat block.

So while the UA version and the (incorrect) DDB version talk about the creature assuming a level, this isn't even defined in the rules, so the correction in the printing makes sense.

Answer 2

My first inclination is to say “no”, since it’s a beast spirit, not an ordinary beast. The fact that the Bestial Spirit does not have a CR given, and its power varies with the spell slot level it is cast at, makes it difficult to judge as well.

I think the great majority of DMs would stop there and just say “no, pick an animal”.

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My second inclination is to say “yes”, because I prefer to facilitate characters being able to do unusual things if it fits into their concept. So if a player really wanted to play a beast spirit druid, I’m sure it could be worked out.

• (a) Druids are limited to changing into forms they have seen, so I’d want a plausible explanation as to how the druid in question became familiar with beast spirits and not just beasts. Or we could run an adventure where that happens somehow.
• (b) You’d have to abide by the limits (e.g. land only to start, water after 4th level, air after 8th), and such.
• (c) We’d have to calculate the effective CR of the baseline beast spirit, and you would have to have your Wild Shape power be able to exceed that CR’s limit to be able to use the form.
• (d) Then as the druid advances and is able to Wild Shape into higher-CR beasts, we’d have to figure it out at each spell level, and define how tough a beast spirit they could become.

So it would be a bit of a pain, but the whole point of playing D&D is to create, develop, and play a character that meets your vision, so as a DM, I’m down with helping make that happen.