from what i can tell, dragons can transform into their humanoid forms at will.
if i cast true polymorph on myself and hold concentration for the full hour, can i then transform between normal bard form and dragon form at will?
Technically, the shapechange features of either 2014 or 2024 dragons key off of Challenge Rating, and so cannot turn into PCs since character sheets do not have a Challenge Rating.
from what i can tell, dragons can transform into their humanoid forms at will.
if i cast true polymorph on myself and hold concentration for the full hour, can i then transform between normal bard form and dragon form at will?
Technically, the shapechange features of either 2014 or 2024 dragons key off of Challenge Rating, and so cannot turn into PCs since character sheets do not have a Challenge Rating.
Yes, and quite apart from that, it really doesn't seem like the intent of any of this is to effectively give a PC the ability to cast a ninth-level spell as many times as they want whenever they want.
Buddy with Suggestion or you with Mass Suggestion. (You need it to not eat your concentration).
Blow through its legendary resistances
Suggest "stop fighting, be a willing recipient for a spell, then voluntarily fail the next saving throw against a non-damaging effect" (That certainly sounds achievable, so it's a valid suggestion)
Cast Nystul's Magic Aura on the dragon to make it count as a Humanoid.
Cast Magic Jar, and take possession of the dragon's body. (It will voluntarily fail the save as per the suggestion).
Now, strangely enough, this doesn't actually get you all of the dragon's features in 2024. It does get you the dragon's hp, HD, str/dex/con, speeds, and senses. But you do retain all your features, including racial features strangely enough, and that means you can still cast spells. (Talk to your DM about if you get anything else; it is a little weird that you end up with this big mouth full of teeth, and these large claws, but your unarmed strike still does just 1 point of bludgeoning damage + strength.)
You can cast Magic Jar a second time whenever you need to do so to repossess your body without returning the dragon's body to it. Or you could use Shapechange or similar to resume human form when you need to do so. (Amusingly, you can also shapechange your dragon body into... a dragon, and get temp hp on top of your dragon hp + their actual abilities like attack routine and breath attack).
I recommend leaving your original body somewhere with a Sequester Spell and a Glyph of Warding containing a Deathward spell, both set to trigger when your soul returns to your body. (In 2024 rules, if the jar is broken and your body is >100' away, your soul first returns to your body, then dies. So the Deathward triggers first and prevents your death, then the Sequester ends and you're free to act, but your body has been perfectly preserved).
A bard is one of the few ways to do all these things by himself, because of Magical Secrets.
Note that the target of Magic Jar is the original body, so you can't dispel the jar or the possessed target (because the magic is in neither place), only the original body (which is safely sequestered somewhere), so Dispel Magic should not be a problem.
Finally, Magic Jar only targets the possessed body at the moment of possession, so you don't need to dutifully cast Nystul's for 30 days to make it permanent. Once you're in possession, you're free to allow it to lapse.
from what i can tell, dragons can transform into their humanoid forms at will.
if i cast true polymorph on myself and hold concentration for the full hour, can i then transform between normal bard form and dragon form at will?
Technically, the shapechange features of either 2014 or 2024 dragons key off of Challenge Rating, and so cannot turn into PCs since character sheets do not have a Challenge Rating.
Yes, and quite apart from that, it really doesn't seem like the intent of any of this is to effectively give a PC the ability to cast a ninth-level spell as many times as they want whenever they want.
pronouns: he/she/they
well, would have been nice for when i run out of spell slots
If you really want to be a dragon:
Now, strangely enough, this doesn't actually get you all of the dragon's features in 2024. It does get you the dragon's hp, HD, str/dex/con, speeds, and senses. But you do retain all your features, including racial features strangely enough, and that means you can still cast spells. (Talk to your DM about if you get anything else; it is a little weird that you end up with this big mouth full of teeth, and these large claws, but your unarmed strike still does just 1 point of bludgeoning damage + strength.)
You can cast Magic Jar a second time whenever you need to do so to repossess your body without returning the dragon's body to it. Or you could use Shapechange or similar to resume human form when you need to do so. (Amusingly, you can also shapechange your dragon body into... a dragon, and get temp hp on top of your dragon hp + their actual abilities like attack routine and breath attack).
I recommend leaving your original body somewhere with a Sequester Spell and a Glyph of Warding containing a Deathward spell, both set to trigger when your soul returns to your body. (In 2024 rules, if the jar is broken and your body is >100' away, your soul first returns to your body, then dies. So the Deathward triggers first and prevents your death, then the Sequester ends and you're free to act, but your body has been perfectly preserved).
A bard is one of the few ways to do all these things by himself, because of Magical Secrets.
Note that the target of Magic Jar is the original body, so you can't dispel the jar or the possessed target (because the magic is in neither place), only the original body (which is safely sequestered somewhere), so Dispel Magic should not be a problem.
Finally, Magic Jar only targets the possessed body at the moment of possession, so you don't need to dutifully cast Nystul's for 30 days to make it permanent. Once you're in possession, you're free to allow it to lapse.
The bit about the saving throw is getting a bit meta for in-game instructions.
They can voluntarily choose to do it, so there must be some way to express it in-world.