Are the plants animated by an Assassin Vine considered magical?

Question

In our last play session the party was attacked by an Assassin Vine. The low-strength kobold ranger was trapped in the vines for several rounds (in part because he went unconscious from damage, but that's beside the point of this question). The party wizard had "Wither and Bloom" but did not use it. However, we are in the jungles of Chult - this was not the first Assassin Vine we have seen and I doubt it will be the last. It would be good to know if we could use Wither and Bloom to free someone if needed.

Wither and Bloom says (emphasis mine):

You invoke both death and life upon a 10-foot-radius sphere centered on a point within range...Nonmagical vegetation in that area withers.

The Assassin Vine's Entangling Vines feature says (emphasis mine):

The assassin vine can animate normal vines and roots on the ground in a 15-foot square within 30 feet of it. These plants turn the ground in that area into difficult terrain. A creature in that area when the effect begins must succeed on a DC13 Strength saving throw or be restrained by entangling vines and roots. A creature restrained by the plants can use its action to make a DC13 Strength (Athletics) check, freeing itself on a successful check. The effect ends after 1 minute or when the assassin vine dies or uses Entangling Vines again.

The vines surrounding the ranger began as non-magical, at which point they were animated by the Assassin Vine's ability. If they are still non-magical, it seems like Wither and Bloom could then have been used to wither them and free the ranger. But if animating them made them magical, Wither and Bloom would not have worked on them.

The Sage Advice Compendium contains the litmus test for whether something is considered magical:

• Is it a magic item?

No.

• Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?

Maybe? What does 'mentioned' mean? Certain the text does not say that the Assassin Vine 'casts the entangle spell'. But does the similarity of the name and the mechanics of the feature resemble Entangle enough to count as it having been 'mentioned'?

• Is it a spell attack?
• Is it fueled by the use of spell slots?

No and No.

• Does its description say it’s magical?

Maybe? The word "magical" does not appear anywhere in the description, but "animates" does. With no 5e definition for what "animates" means, we fall to common English usage - but that includes both the senses of imparting normal and magical movement depending on context.

I note that the Animated Objects described in the Monster Manual:

are crafted with potent magic to follow the commands of their creators...The magic that animates an object is dispelled when the construct drops to 0 hit points

Further, all three of them have:

Antimagic Susceptibility. The armor is incapacitated while in the area of an antimagic field. If targeted by dispel magic, the armor must succeed on a Constitution saving throw against the caster's spell save DC or fall unconscious for 1 minute.

This suggests that "animated" might be a synonym for "magical". Then again, perhaps that only works when creating creatures from objects rather than simply making non-magical plants move.

Are the plants animated by an Assassin Vine considered magical while animated?
Are they subject to withering by Wither and Bloom?

Answer 1

They are not magical.

Three out of five items provided by the Sage Advice Compendium for testing if something is magical or not are easy to check. The other two, as posed in the question, may require some clarification.

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Is it a spell? Or does it let you create the effects of a spell that’s mentioned in its description?

No, it is not a spell and even if it recreates the effect of Entangle, such spell is not mentioned. For the meaning of "mentioned" you can compare, for example, the Antimagic Cone of a Beholder (emphasis mine):

Antimagic Cone. The beholder’s central eye creates an area of antimagic, as in the antimagic field spell, in a 150-foot-cone. At the start of each of its turns, the beholder decides which way the cone faces and whether the cone is active. The area works against the beholder’s own eye rays.

or the Chuul's Sense Magic¹ trait (emphasis mine):

Sense Magic. The chuul senses magic within 120 feet of it at will. This trait otherwise works like the detect magic spell but isn't itself magical.

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Does its description say it’s magical?

No, the description does not say that this ability imbues the vines with magic. From a in-world point of view, it seems that the Assassin Vine can command the plants to entangle, as, for example, a Beast Master ranger can command their companion to attack. In this case, "animate" means to "make move and do things".

As noted, "animated" is not a game term, and it may not automatically mean "magical". Some monsters can animate objects and/or creatures, and the description clearly state that this is done by magic: check the Animate Trees trait of Treants (emphasis mine):

Animate Trees (1/Day). The treant magically animates one or two trees it can see within 60 feet of it.

Another example is the Animate Chains of a Chain Devil (emphasis mine):

Animate Chains (Recharges after a Short or Long Rest). Up to four chains the devil can see within 60 feet of it magically sprout razor-edged barbs and animate under the devil's control, provided that the chains aren't being worn or carried

Since Assassin Vine trait does not explicit that the Entangling Vines are magically animated, they are not magical.

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Regarding the Animated Objects monster.

The Animated Objects entry of the MM clearly state that such objects are magical:

Animated objects are crafted with potent magic to follow the commands of their creators.

and they are subject to Antimagic Field. Moreover, the Animated Armor has this bit of text (emphases mine):

Ponderous but persistent, this magical guardian is almost always a suit of plate armor. To add to its menace, animated armor is frequently enchanted with scripted speech, so the armor can utter warnings, demand passwords, or deliver riddles. Rare suits of animated armor are able to carry on an actual conversation.

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¹ Note that the spell is mentioned, but the ability is not magical: this is an example for what "mentioned" in the SAC means.