[RPG] the spell save DC and spellcasting modifier for a Rogue with Magic Initiate

dnd-5efeatsroguespells

As a rogue I'm planning to take Magic Initiate with warlock class. The Magic Initiate feat says:

[…] Your spellcasting ability for these spells depends on the class you
chose: Charisma for warlock […]

  • cantrip 1: Booming blade or Green flame blade
  • cantrip 2: Minor illusion
  • 1st-level spell: Hex

My stats bonuses are:
STR : -3 | DEX +6 | INT 0 | WIS +1 | CHA +4 | prof : 4

Questions:

  • Green flame blade :

[…] The second creature takes fire damage equal to your spellcasting
modifier. […]

What is my spellcasting modifier? 0 from INT as rogue or +4 from CHA as warlock?

  • Minor illusion :

[…] If a creature uses its action to examine the sound or image, the
creature can determine that it is an illusion with a successful
Intelligence (Investigation) check against your spell save DC. […]

What is my spell save DC? 12 (8 + 0 from INT + 4 from prof) or 16 (8 + 4 from CHA + 4 from prof)?

Best Answer

Your spellcasting modifier for those spells you cast using Magic Initiate is Charisma

You quoted the relevant text:

Your spellcasting ability for these spells depends on the class you chose : Charisma for warlock

So your DCs, to hit modifiers, etc. for those spells are all based on your Charisma, so: DC 16.

If you later learn those same cantrips from another source (multiclassing, Arcane Trickster roguish archetype) you can choose which ability score to use, if that second source uses a different ability score for casting. If you have the Arcane Trickster archetype, then your spellcasting ability for your rogue spells is Intelligence.

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