As long as the cops are pure mook-grade NPCs and they concentrate themselves into a fairly small number of zones, then even a fairly modest evocation is enough to take them down. For example, if you define "the front yard" as a zone, and "the back yard" as a second zone, and stipulated that the 200 cops were packing themselves into those two zones to get into the house, then all you would need is maybe a 5 shift evocation (assumptions: weapon:1, 2 zone spell with control of 7 or so vs cops with armor:2, defense or perhaps 2, and no consequences).
However, I think that this is poor application of zone rules, and downright silly tactics on the part of the cops. My thinking is that every half-dozen targets, tops, should constitute a "zone" (redefining the zones for tightly packed masses as needed -- ), and that in any case the cops would be fairly spread out even without this sort of adaptive zoning, enough that there would probably be fairly few zones with more than a handful of cops packed into them. So the 200 cops might require a 30-40 zone effect, which is ... non-trivial.
Sometimes you need numbers.
Agreed. But I think that Richard is trying to say is that sometimes it's best
not to have numbers -- or that sometimes the numbers aren't relevant. And I agree with that.
Say, for example, a group of PCs learns that there is a nuclear warhead headed at them. It is valid for the GM to dictate that the only way to escape the blast is to not be in the fireball when it goes off (run like mad, escape into the Nevernever, or whatever) -- and that a magical shield of any strength that can be produced in the time available
just won't cut it. In such a case, putting numbers to it is just throwing down the gauntlet for the rules lawyer in the party to prove you wrong.
