I don’t understand what your saying @Medix2

I’ll come back to this.

Why would the robed of the arch magi work and the rod of the pact keeper not work? I get that if I'm a multi class warlock/other caster, the rod of the pact keeper will ONLY raise my warlock save dc while the robes will raise both/all of them, but then if I'm a multi class warlock, I'd use my warlock save dc for the familiar's save dc, not my other class(es) save dc, correct?

@Skavies I’ll edit in more detail about that, one moment.

@Skavies Is that more clear?

Yes, it is more clear. I'm going to have to think about it for a while, something is still not quite clear, but I'm unsure of what it is. I like your answer, it makes sense, but it just doesn't quite feel correct. Thank you very much.

I got it. The rod of the pact keeper says " +1 bonus to spell attack rolls and to the saving throw DCs of your warlock spells." The robes say "Your spell save DC and spell attack bonus each increase by 2." The difference besides the +1 and the +2 are that the robes apply to the dc of all spells, not limited to warlock only spells. So I'm still not convinced that one would work and not the other. Both are limited to spells only so either both should work, or neither should work.

Robe of the Archmagi is not limited to spells only. It just increases your spell save DC, which can be used for things other than spells. It does not specify a use case at all. On the other hand, rod of the pact keeper does specify that it only increases the DC for your spells specifically.

Thank you, now it makes sense. I thought the spell save dc only affected spells. If there are other uses for it besides this new Tasha's invocation, then your answer makes perfect sense.

Spell save DC is just a number on your character sheet. There are lots of non-spell features that reference it.

I've only been playing 5e for about a year. Started with D&D basic set about 40 years ago, but still don't know much of 5e.

I did not know your save dc affected anything beyond spells.

Now you've got me curious on what else I can use my save dc for.

Most of the non spell features that use it are going to be magic items with spell like effects.

Then I'm guessing that those magic items with spell like effects would not be affected by a rod of the pact keeper, but would by the robes?

That is correct. I’ve got an example, one second

Not the best example, robe of the Archmagi doesn’t affect this either.

As far as I am aware, magic items have a dc set in the item. Even scrolls are set by the spell level stored in them, not the dc of the mage type creating them. Ring of spell storing will store the dc of the caster who put the spell in it, but that's still just spell casting.

@ThomasMarkov Can you provide some examples of the spell save DC being used for something other than spells (excluding this invocation?)

I feel that it would improve your answer

Yeah, I’m going to Popeyes right now.

Mmmm, chicken

I have a Popeyes down the hall from my office.

I'm not as surprised by that as I expect I should be, considering what your line of work is

@RevenantBacon Okay, added an example.

I find this acceptable. It still doesn't feel right, but I find your logic to be accurate.

My question is: what ways can the familiar force a saving throw?

Ah. looks like all of the chain pact familiars have abilities that force saves.

I was gonna point out Imps and Sprites with their poison

It's actually a major upgrade, especially for the Sprite, as a free KO attempt on every enemy is really good, but the DC 10 save keeps it in check

I think it also boosts the Ravens Mimicry ability, but I don't remember if that's opposed or a flat DC

Also all of the Instruments of the Bard, so a Bard who took a 1 level hexblade dip using instrument of the bards is another case.