When a mystic theurge uses the Combined Spells feature, what's the spell level?

Question

I asked a related but different question here: How does the Mystic Theurge's Combined Spells feature work?

In the following scenario, how does a mystic theurge's combine spells ability work? Cleric 3 / wizard 3 / MT 3. They use a second level wizard slot to cast a first level cleric spell. Lets assume that the character has wisdom 18 for +4 and int 20 for +5.

• Which attribute is used in calculating the save DC: the cleric's +4 due to cleric spell, or wizard's +5 due to wizard spell slot?
• What is the DC per the level of spell? Since it's Cleric 1, is it +1 or slot 2 for +2?

The end DC can be 15, 15, 16, or 17 depending on how the abilities work.

Answer 1

Your Cleric spell cast as a Wizard would use the Wizard's Spell slot and Int for the DC, resulting in the DC 17.

The Combining Spells class feature includes this line at the end of it's first section, which dictates this answer

The components of these spells do not change, but they otherwise follow the rules for the spellcasting class used to cast the spell.

Therefore you would need to follow any rules about casting with the desired class, but could also gain the benefits of increasing DC. Honestly, it's the least they can do given how hyper-specialized Mystic Theurge is about spellcasting (giving up advancement on other class features).