You've played MHRP, haven't you? So you know what the rules are (pages OM6, OM18, OM55):
WHEN TO ROLL THE DICE
When you roll the dice, the Watcher or another player rolls their dice in response to see how things work out. Any time
there’s a meaningful choice to make, you can bring out the dice. Not every situation needs you to “roll the bones,” however. Use the following lists as a guide for when dice are appropriate.
Roll the dice when…
*You’re not sure if your hero will succeed or fail.
*You want to try something that’s bold, challenging, or dangerous.
*You want to oppose, challenge, or thwart another character.
*You want to show off your hero’s super-powers or cool abilities.
Don’t roll the dice when…
*The outcome isn’t an interesting part of the story.
*There’s no risk, challenge, or threat involved.
*The only outcome of either success or failure is that nothing happens.
*There’s nothing or nobody to stop your hero from doing something.
*The situation is outside your hero’s ability to change.
. . .
THE DOOM POOL AS OPPOSITION
The doom pool stands in as the opposition dice pool for anything the heroes want to try that‘s important enough to break out the dice but for which no opposing characters are present. Natural forces, sheer luck, that growing sense of dramatic tension - the doom pool acts as a generic pool of opposition when the situation demands it.
. . .
Automatic Success
If you have a power that might be useful in eliminating an asset, complication, or some other trait, you might be able to forego the roll entirely and just spend 1 PP to succeed automatically. This works the same way heroes with a Stamina power trait can spend 1 PP to eliminate stress. Most of the time, this only works when your hero has either the time or the freedom to do this without interference, and the Watcher should already have established that you’d need to roll the dice as opposed to simply letting you get what you want.
When you roll the dice, the Watcher or another player rolls their dice in response to see how things work out. Any time
there’s a meaningful choice to make, you can bring out the dice. Not every situation needs you to “roll the bones,” however. Use the following lists as a guide for when dice are appropriate.
Roll the dice when…
*You’re not sure if your hero will succeed or fail.
*You want to try something that’s bold, challenging, or dangerous.
*You want to oppose, challenge, or thwart another character.
*You want to show off your hero’s super-powers or cool abilities.
Don’t roll the dice when…
*The outcome isn’t an interesting part of the story.
*There’s no risk, challenge, or threat involved.
*The only outcome of either success or failure is that nothing happens.
*There’s nothing or nobody to stop your hero from doing something.
*The situation is outside your hero’s ability to change.
. . .
THE DOOM POOL AS OPPOSITION
The doom pool stands in as the opposition dice pool for anything the heroes want to try that‘s important enough to break out the dice but for which no opposing characters are present. Natural forces, sheer luck, that growing sense of dramatic tension - the doom pool acts as a generic pool of opposition when the situation demands it.
. . .
Automatic Success
If you have a power that might be useful in eliminating an asset, complication, or some other trait, you might be able to forego the roll entirely and just spend 1 PP to succeed automatically. This works the same way heroes with a Stamina power trait can spend 1 PP to eliminate stress. Most of the time, this only works when your hero has either the time or the freedom to do this without interference, and the Watcher should already have established that you’d need to roll the dice as opposed to simply letting you get what you want.
Bobby is on a date with one of the B.A.D girls (I can't remember now which of Black Mamba, Asp or Diamondback), in Washington DC. Bobby's player declares that he is going to freeze the Reflecting Pool. This is Bobby showing off his cool abilities. Given that he has Ice Mastery, freezing the reflecting pool is within his ability to change (this does not exceed the capacity to generate city-wide effects by freezing water). Given that no character is opposing the attempt, I as GM roll the Doom Pool as opposition. (The possibility of spending a PP for automatic success was not canvassed, as best I recall.)
There is no need for any house rule. And there is no need for damage types. There is just adjudication of the declared action by reference to (i) fiction (ie the Reflecting Pool is water that can be frozen) and (ii) thematic significance (ie here is Bobby showing off his cool abilities).
The freezing of the Reflecting Pool has not come up again. (Would anyone expect it to?) If it did, maybe no roll would be called for, because it would not on this occasion count as showing off cool abilities (that had already been done, and doing it a second time isn't really showing off any more).
What is the mooted house rule? I applied the actual, written rules. (Which I've quoted, in this and previous posts.) And - to reiterate - determining that the Reflecting Pool is water that might be frozen by an ability to create city-wide ice/cold effects is not a house rule. Any more than noting that (say) an elephant is big enough to block a narrow road is a house rule. Or that one can knock on a door to create noise is a house rule.
