Mystic Theurge

[Rakoa]

How would one pull of a Mystic Theurge build? Right away, I just think of a Cleric 10 / Wizard 10 multiclass, using lower-levelled spells with all of those big spell slots, but how would that work in practice? I question the viability of such a build in any portion of the game. What are the thoughts of the community?

[Visser3SansTheP]

How would one pull of a Mystic Theurge build? Right away, I just think of a Cleric 10 / Wizard 10 multiclass, using lower-levelled spells with all of those big spell slots, but how would that work in practice? I question the viability of such a build in any portion of the game. What are the thoughts of the community?

Favoured soul and arcana cleric do a reasonable imitation. Otherwise decide what you're actually trying to achieve by being a mystic theurge and question whether a lore bard couldn't do the same thing but better.

[Ninja_Prawn]

How would one pull of a Mystic Theurge build? Right away, I just think of a Cleric 10 / Wizard 10 multiclass, using lower-levelled spells with all of those big spell slots, but how would that work in practice? I question the viability of such a build in any portion of the game. What are the thoughts of the community?

It's tough. Maybe a prestige class is the way to go. JNAProductions homebrewed one a while back that you could look up.

The problem is that 5e is very carefully balanced, which means the classic mystic theurge thing of 'more spell slots' can't really be imported in any meaningful way. And multiclassing doesn't work because of the viability questions you've already raised.

Perhaps one way to do it would be to start from the sorcerer chassis, then take away all the metamagic and add in some divine casting. More than the favoured soul gets, and maybe as many total spells known as the wizard?

[Starsinger]

How would one pull of a Mystic Theurge build? Right away, I just think of a Cleric 10 / Wizard 10 multiclass, using lower-levelled spells with all of those big spell slots, but how would that work in practice? I question the viability of such a build in any portion of the game. What are the thoughts of the community?

Small thing, but go 11/9 (your choice which is which), so you get 6th level spells on one of them and still 5th on the other.

[Serket]

How would one pull of a Mystic Theurge build?

Raw, I have no idea. Cleric (some small number)/Sorceror (favoured soul) some larger number?

Homebrew: Given how 5e works, a mystic theurge would have the same full-caster spell slot progression everyone else does. What happens if you start with a sorceror chassis and swap metamagic for the ability to take spells known from the cleric list (as well as the sorc one)? Does that break anything, and would it be viable?

[Giant2005]

How would one pull of a Mystic Theurge build? Right away, I just think of a Cleric 10 / Wizard 10 multiclass, using lower-levelled spells with all of those big spell slots, but how would that work in practice? I question the viability of such a build in any portion of the game. What are the thoughts of the community?

The Cleric's best spells are low level, the Wizard's best spells are high level.
Whether or not it is a viable combination depends entirely on your outlook - you could consider yourself a pretty amazing Cleric with some extra Wizard utility, or you could consider yourself a lousy Wizard with a religion that is holding back his spellcasting potential.

[Dimolyth]

How would one pull of a Mystic Theurge build? Right away, I just think of a Cleric 10 / Wizard 10 multiclass, using lower-levelled spells with all of those big spell slots, but how would that work in practice? I question the viability of such a build in any portion of the game. What are the thoughts of the community?

Well it is about what exactly you would like to achive?

On my 3.5 campagn, I had been playing a Mystic Theurge character cleric3/wizard3/mystic theurge4/olin gisir2 (the latter is specific faerunian elven arcane loremaster). The cleric domaines of choice were Plant and Animal, the choice of spells were almost 80% buffes and controls.

While translating it to the 5e, I ended with a Nature Cleric5/Abjuration Wizard X - unoptimized build, but it gets everything the character had used to.
Lore bard, Favored Soul sorcerer and Arcana Domain cleric could be more powerful, but they just worked differently mechanically and flavorwise.
The were lack of spell known, lack of signature spells of the character...

So as an answer I would tell: it depends on how do you see Mystic Theurge and what do you expect of him. Due to this reponse, several builds could be used:
Arcana Domain Cleric
Lore Bard
Favored Soul Sorcerer
Cleric with Ritual Caster(wizard)
Cleric/Wizard combination (the propotions of either class could be from 1/19 to 10/10)
Or more complex solutions (lore bard/favored soul sorcerer?)