Hero into Dragon into Archmage rinse repeat

[Balfore]

Okay, here's the official rule from the introductory section of the Monster Manual (or the DM's Basic Rules):

"SPELLCASTING
A monster with the Spellcasting class feature has a spellcaster level and spell slots, which it uses to cast its spells of 1st level and higher (as explained in the player's D&D basic rules and the Player's Handbook)..."

So you cannot use the Spellcasting trait from any statblock, because all of the shapechanging options in the game (as far as I'm aware of) specifically prohibit you from using class features.

You can use the Innate Spellcasting feature unless something else tells you you can't, however.

Interestingly, the Spellcasting trait is the only one called out as a class feature in monster statblocks. One might assume that something like Sneak Attack on the assassin would count as a class feature too...but that becomes problematic. For example, that would mean that a creature could polymorph into a CR 6 Hobgoblin Warlord and get 4d6 Martial Advantage, but not into a CR 5 Master Thief and get 4d6 Sneak Attack.

There are other examples. The major problem is that the NPC statblocks in the appendices are not substantially different than the NPC statblocks included as parts of monster entries (such as Hobgoblins and Drow). So if you take "has the same name as a class ability" as the standard, you end up with really arbitrary and inconsistent restrictions that drive you to transform into hobgoblins and drow instead of half-orcs and high elves, because the former have monster entries and special abilities that you can use and the latter don't.

I stick with the most conservative restriction to avoid that problem. Anything in a monster statblock (including the NPC statblocks in the appendices) is by definition a monster ability, not a class ability, unless something says otherwise. The only one that fits that bill is Spellcasting, which has been explicitly defined as a class feature.

As an alternative, you might note that the Spellcasting class feature lists a class and level in its description. You could use the same rules for other features: if the statblock says that it uses the feature as a character of a certain class and level, then it you could count it as a class feature. Off the top of my head, I can't recall any features that do that other than Spellcasting, but I may be missing something in the Volo's Appendix.

Honestly, I think that's probably how the designers intended it. They didn't care if a dragon turned into a hobgoblin or an assassin, but they didn't want monsters picking up spellcasting with the Change Shape feature. They phrased it as "class ability" and defined Spellcasting as being such, in order to be clear that it applied to Spellcasting, while leaving space for adding other class abilities to monsters in the future by calling them out as such--future compatibility with Change Shape.

Such a great explaination! Thank you so much!

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[Balfore]

Thanks for all the good comments.
Change Shape is covered.

So, can he use True Polymorph to do the same thing. Turn into an Archmage, or is this all the same principal ruling?

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[jaelis]

Thanks for all the good comments.
Change Shape is covered.

So, can he use True Polymorph to do the same thing. Turn into an Archmage, or is this all the same principal ruling?

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Same principle ruling, no "class" features. That's how I would play it any way.

 

[Sword of Spirit]

So, can he use True Polymorph to do the same thing. Turn into an Archmage, or is this all the same principal ruling?

As written, there is nothing to prevent them gaining the class features of the form they take, and since you need to be a 17th level caster to take this spell, there probably isn’t too much of an issue. However, I’d personally house rule it to disallow class features.

 

[Ovinomancer]

Okay, here's the official rule from the introductory section of the Monster Manual (or the DM's Basic Rules):

"SPELLCASTING
A monster with the Spellcasting class feature has a spellcaster level and spell slots, which it uses to cast its spells of 1st level and higher (as explained in the player's D&D basic rules and the Player's Handbook)..."

So you cannot use the Spellcasting trait from any statblock, because all of the shapechanging options in the game (as far as I'm aware of) specifically prohibit you from using class features.

You can use the Innate Spellcasting feature unless something else tells you you can't, however.

Interestingly, the Spellcasting trait is the only one called out as a class feature in monster statblocks. One might assume that something like Sneak Attack on the assassin would count as a class feature too...but that becomes problematic. For example, that would mean that a creature could polymorph into a CR 6 Hobgoblin Warlord and get 4d6 Martial Advantage, but not into a CR 5 Master Thief and get 4d6 Sneak Attack.

There are other examples. The major problem is that the NPC statblocks in the appendices are not substantially different than the NPC statblocks included as parts of monster entries (such as Hobgoblins and Drow). So if you take "has the same name as a class ability" as the standard, you end up with really arbitrary and inconsistent restrictions that drive you to transform into hobgoblins and drow instead of half-orcs and high elves, because the former have monster entries and special abilities that you can use and the latter don't.

I stick with the most conservative restriction to avoid that problem. Anything in a monster statblock (including the NPC statblocks in the appendices) is by definition a monster ability, not a class ability, unless something says otherwise. The only one that fits that bill is Spellcasting, which has been explicitly defined as a class feature.

As an alternative, you might note that the Spellcasting class feature lists a class and level in its description. You could use the same rules for other features: if the statblock says that it uses the feature as a character of a certain class and level, then it you could count it as a class feature. Off the top of my head, I can't recall any features that do that other than Spellcasting, but I may be missing something in the Volo's Appendix.

Honestly, I think that's probably how the designers intended it. They didn't care if a dragon turned into a hobgoblin or an assassin, but they didn't want monsters picking up spellcasting with the Change Shape feature. They phrased it as "class ability" and defined Spellcasting as being such, in order to be clear that it applied to Spellcasting, while leaving space for adding other class abilities to monsters in the future by calling them out as such--future compatibility with Change Shape.

Excellent summation, mostly agree. My only point is that I wouldn't allow a character to true polymorph or shapechange into a hobgoblin warlord or a master rogue. Both effects pick a creature type, not specific creatures. So you could choose hobgoblin, and become a hobgoblin, but not a warlord of hobgoblins. Same with any humanoid -- you can become that humanoid, but not a master rogue. Those are too specific of an example, it would be like allowing the spell to turn you into Bob, that guy over there, and bam, you're Bob. So, you could pick a type of creature, and that offers a great deal of flexibility, and some truly awesome forms, but limits it a bit from picking the ones that are suped up versions of a base creature (this would cover Githyanki Knights, as well -- you could be githyanki, but knights are advanced githyanki, not something altogether different).

 

[Sunseeker]

Polymorph only lets you access the "base" creature. So your dragon can become a human...who can then go to wizard school. But he can't just turn into someone who knows spells.

Creatures with spell-like abilities? Yeah he'll get those.

This is again one of those problems that only shows up when you design humanoid NPCs like "monsters". If it could be a humanoid with a class, it should be built like a humanoid with a class. If it's an intelligent creature with a class-like feature, just give it the class feature.

 

[Sword of Spirit]

Excellent summation, mostly agree. My only point is that I wouldn't allow a character to true polymorph or shapechange into a hobgoblin warlord or a master rogue. Both effects pick a creature type, not specific creatures. So you could choose hobgoblin, and become a hobgoblin, but not a warlord of hobgoblins. Same with any humanoid -- you can become that humanoid, but not a master rogue. Those are too specific of an example, it would be like allowing the spell to turn you into Bob, that guy over there, and bam, you're Bob. So, you could pick a type of creature, and that offers a great deal of flexibility, and some truly awesome forms, but limits it a bit from picking the ones that are suped up versions of a base creature (this would cover Githyanki Knights, as well -- you could be githyanki, but knights are advanced githyanki, not something altogether different).

I know why you'd say that, and I understand the theoretical appeal/logic. However, it is problematic when it comes to practicality. You'd have to go through every humanoid in the Monster Manual and decide which statblocks (if any) count as a base creature, and which count as an advanced version. Can you use the basic "Goblin" statblock? That really represents goblin warriors. Your typical goblin is just a commoner with some goblin racial traits. The same goes for most humanoids (see published 5e adventures for evidence of this). How does that apply to creature types other than humanoids? Are all adult Centaurs running around with 6d10 HD, and all Cambions packing 11d8 HD with proficiency in Deception, Medium Armor, and Spears (amongst others)? If not, how many HD does a base centaur or cambion have? There just isn't a really good (simple and consistent) place in 5e's mechanical presentation to make a dividing line between statblocks and say which should count as shapeshift-able creatures, and which shouldn't. Or at least, if there is I'm not sure where it lies.

 

[FrogReaver]

Ancient metallic Dragons have change shape, which doesn't care about the spell casting trait, only class abilities, and since all creatures in the monster manual are in essence, not creatures advancing in classes, you should be able to use the spellcasting from the archmage monster.

I think it would be up to the DM to determine if some ability in the monster manual counts as a class feature or simply an ability. The Monster Manual doesn't really spell out how such things are to be treated. And always remember that just because something isn't said you can't really assume anything about it one way or the other.

So I want to ask. What evidence do you have that the archmage abilities are not class abilities?

 

[ad_hoc]

Everything else aside, the game is supposed to be broken at levels 17+.

The party is expected to take on threats to the entire multiverse.

 

[Ovinomancer]

I know why you'd say that, and I understand the theoretical appeal/logic. However, it is problematic when it comes to practicality. You'd have to go through every humanoid in the Monster Manual and decide which statblocks (if any) count as a base creature, and which count as an advanced version. Can you use the basic "Goblin" statblock? That really represents goblin warriors. Your typical goblin is just a commoner with some goblin racial traits. The same goes for most humanoids (see published 5e adventures for evidence of this). How does that apply to creature types other than humanoids? Are all adult Centaurs running around with 6d10 HD, and all Cambions packing 11d8 HD with proficiency in Deception, Medium Armor, and Spears (amongst others)? If not, how many HD does a base centaur or cambion have? There just isn't a really good (simple and consistent) place in 5e's mechanical presentation to make a dividing line between statblocks and say which should count as shapeshift-able creatures, and which shouldn't. Or at least, if there is I'm not sure where it lies.

Well, I find it's pretty easy to find a midpoint between not allowing polymorph to select goblins bosses and having to figure out the entire demographic make-up of the goblin race to determine a statistical average: its called "goblin" and it's in the Monster Manual.

As an aside, under the description of Legendary Creatures, it states that if you assume the form of a legendary creature you do not get the legendary abilities, so no legendary actions or resistances if you True Polymorph into an Ancient Brass Dragon.