How do you roll a prof with no prof?
...its a skill check.
So roll 2d20 take the lowest nothing adds and you aren’t saying the DC.
I can’t imagine you calling out other DMs for being bad at improv if this is what you got.
I don't have to tell you the DC, but by context it would be fair to assume Id say 30.
You're trying to replicate a spell by waving a sword around. All you're really doing is attempting to cast the spell. That is an Arcana check.
What does "no mods" mean? Is this you just saying the player can't use anything that can possibly cause them to reach DC 30?
Yes.
I think he just means “I said I can’t tell you it’s impossible and I don’t like the DCs being between 5 and 30 and a fighter can take a feat for a skill prof and expertise so at level 17 they have 12 plus stat to that roll so I need to make something up where that can’t happen”
This was predictable.
I would like you to point out where in Improvise Action's text it says you're guaranteed a particular outcome.
If you're a Martial attempting to literally cast a spell by just waving your sword around, you aren't going to get that outcome.
Now if you were a half-caster, then theres room to say yes, you can add your modifiers, because by virtue of being at least part caster you don't need to make a substantive pitch to justify doing something you can already do.
And Im also going to just sit back and relish in the sheer irony of trying to say Im bad at Improv when the example in question is "I wave my sword around and cast a spell i get that right????"