For some reason I’ve just become obsessed with bulettes and I want to play a character that can turn into one for the new campaign we are starting. I am very new to dnd, so this might be a silly question, and balanced homebrew is on the table. We haven’t decided on what level our party is starting at. Hope someone can help!
Be a high level spellcaster with the True Polymorph spell. Because a lower level character cannot accomplish it alone except with a magic item, and under conditions that are unlikely
Because the bulette is a monstrosity and not a beast, the regular polymorph spell will not work (it is limited to beasts); you need the 9th level true polymoprh. But that spell says:
If you turn a creature into another kind of creature, the new form can be any kind you choose whose challenge rating is equal to or less than the target's (or its level, if the target doesn't have a challenge rating).
The bulette has Challenge Rating 5, so you must be at least a 5th level character if you want to turn yourself into a bulette with this spell. But it is a 9th level spell, and any 5th level character is nowhere near getting 9th level spells. For a Wizard it comes at 17th level. Other options are Bard, Warlock, or Arcane Cleric.
So what else is there, if your GM doesn't want to have you all create 17th level characters? Or if you want to choose a class that can never get 9th level spells, say, Arcane Trickster or Eldritch Knight? Well if you came upon a 9th level spell scroll for True Polymoprh and the spell is on your class spell list, the rules allow you to attempt casting it, with an ability check that would be fairly difficult (DMG p. 200):
Spell Scroll ...If the spell is on your class's spell list but of a higher level than you can normally cast... the DC equals 10 + the spell's level.
So that's DC 19 for true polymorph, and if you fail, the spell disappears from the scroll.
And that spell scroll would let you do this just once. And it is a legendary magic item, which no 5th level character should come across, typically. And you'd need an ongoing supply of such scrolls to make this a "routine" thing for your character.
At lower levels, what other recourse do you have?If your GM is flexible enough, you could beg them to homebrew a magic item that would probably be very rare and require attunement, and would do nothing other than allow the bearer to transform into a bulette for one hour once between each long rest, or the like.
The only other option I can think of is to ask your GM to let druid's wild shape feature be expanded to include monstrosities, but there are strong reasons why that doesn't really fit the game very well, as you can see in answers to this question. Asking for wild shape to be expanded only to bulette (as pointed out by Mołot) would be a humbler request of the GM, and perhaps more realistic, especially if you come up with a character background that renders it plausible (maybe you come from an exotic land where the bulette is a more common, naturally occurring creature in the environment).