Ok, we are playing an intentionally strange and absurd campaign, and we have a lot of odd class combinations and have access to excessively powerful magic items. I have multi-classed my Eldritch Knight and taken one level of Sorcerer, and have access to a Staff of the Magi.
The description of the Spell Save DC to use when casting spells with the staff says this:
While holding the staff, you can use an action to expend some of its charges to cast one of the following spells from it, using your spell save DC and spellcasting ability (DMG, page 203)
I only took the level of sorcerer to be able to use this staff (and a few other minor perks), and therefore my Charisma is much lower than my Intelligence. Normally when casting spells I would use Charisma for spells obtained through sorcerer class, and Intelligence for Eldritch Knight spells. I would like to use Intelligence for the staff, but since it can only use it because I have a level in Sorcerer, does that mean I have to use Charisma for the DC, or can I use Intelligence?