Here's what the actual book says on Improvising:
James Wyatt wrote:Something amazing happened one time I was playing D&D with my 9-year-old son. When we finished an encounter, my son took over. He decided that he was going to search around one of the statues in the room, that he was going to get hit by a trap (an arrow would shoot out at the statue), and that he’d find a treasure there.
Hey, wait a minute. I thought I was the DM!
That was my first reaction. But I bit my tongue. I rolled damage for the trap, and I let him have his treasure. (I determined what it was—I wasn’t about to relinquish that much control.)
He never enjoyed the game more.
I learned the most important lesson about D&D that day. I remembered that this is a game about imagination, about coming together to tell a story as a group. I learned that the players have a right to participate in telling that story—after all, they’re playing the protagonists!
—James Wyatt
There are actually quite a few testimonials like that, the section goes on - mechanics free - for two pages. The things people are actually talking about when they talk about the improvisational guidelines aren't actually in the improvisation section at all. They are simply the sum total of all the mechanics that are actually in the book.
And those mechanics are that the Difficulties and Damage values for actions are listed
by Player Character Level. So we have such opaque charts as the Damage chart on page 185:
Damage by Level
Normal Damage Expressions
Level Low Medium High
1st–3rd 1d6 + 3 1d10 + 3 2d6 + 3
4th–6th 1d6 + 4 1d10 + 4 2d8 + 4
7th–9th 1d8 + 5 2d6 + 5 2d8 + 5
10th–12th 1d8 + 5 2d6 + 5 3d6 + 5
13th–15th 1d10 + 6 2d8 + 6 3d6 + 6
16th–18th 1d10 + 7 2d8 + 7 3d8 + 7
19th–21st 2d6 + 7 3d6 + 8 3d8 + 7
22nd–24th 2d6 + 8 3d6 + 8 4d6 + 8
25th–27th 2d8 + 9 3d8 + 9 4d6 + 9
28th–30th 2d8 + 10 3d8 + 10 4d8 + 10
Yeeeah. That's pretty opaque, right? What the hell are you supposed to do with that? Well, here's the explanation:
DMG, page 184 wrote:Set Damage for Attacks: Use the Damage by Level table to set damage for the monster’s attacks. Most at-will attacks should use the medium normal damage shown on the table. For attacks against multiple targets, the melee attacks of artillery monsters, and controller attacks that also include significant control functions, use the low normal damage column. For attacks that have low accuracy (including brute attacks) and the high-damage attacks of lurker monsters, use the high normal damage column. Use the limited damage expressions for powers the monster can use only once or twice a fight—powers that have encounter recharge or recharge rolls.
But wait! You're probably wondering what the fuck would make you decide to put some thing into one category or the other. And um... it doesn't actually tell you. There is no set of mechanics for that at all. You're just supposed to look at the Monster Manual and figure out a pattern. Seriously, that's their actual suggestion:
DMG wrote:For inspiration, check the powers for creatures in the Monster Manual. That book has a list of monsters by level and role, so you can quickly look up other creatures that are similar to your new monster. Then either choose some powers that seem right, modifying them as needed, or create new ones of comparable effect.
So basically there are no rules at all except that there is a list of acceptable damage outputs by character level. That's it. That's the entire "system".
-Username17