Nekkidcarpenter

"A city strength level demon": I have no idea what this means; is this terminology from another game? Does it mean a city-level threat (as opposed to national threat, planetary threat, etc.)?
 
"Punch strong enough to create shockwaves": This isn't a function of strength.  It sounds like an attack with one or more of the advantages "Area of Effect (Cone)" or "Double Knockback".
 
"Dent steel with his blows": Let's go with an I-beam, which has 9 PD and 8 BODY (per 2m). It takes 10 BODY to damage and 17 BODY to break. That requires a strength of 50 or more (to deal a 10d6 punch for 10 BODY on average).
It also implies strength less than 85 (deals a 17d6 punch for 17 BODY on average).  You did specify "dent", not break.
 
"Crater hills": Let's go with Dirt, which has 0 PD and 10 BODY (per cubic meter). I couldn't find the volume of a hill anywhere, so let's go with the volume of a 2 bedroom house (1500 sq ft x 8 ft ceilings = 12,000 cubic feet = 340 cubic meters). Typically each doubling of mass is +1 BODY; to get 340 times the mass of the initial cubic meter, you need 9 doublings (technically x512) for +9 BODY.  So 19 BODY in a single attack will crater dirt equal to the volume of a house.  That requires a strength or 95 or more (to deal 19d6 punch for 19 BODY on average).
 
This is in a different league of strength than denting steel.  It's stronger than Grond, the Hulk of the Champions universe! It's probably way beyond what PCs can handle -- an average punch deals 66 damage! In short, don't let your demon do this with pure strength. Make it an Area of Effect attack that encompasses a hill and deals 10 BODY on average.
 
So... putting all that math aside, its much safer to start with game mechanics (how many d6 does my punch do), figure out the strength from there, and then figure out the types of things they can do with that strength. A standard superheroic campaign runs 6 - 14 damage classes, equivalent to 30 - 70 strength.
 
I think 50 to 60 strength is fine -- pretty standard for the brick archetype -- then maybe slap Area of Effect (Cone) on it for the shockwave/hill cratering effect.  Put some limits on the AoE, though -- charges, or increased endurance cost -- as it represents a super dangerous attack that undoubtedly breaks your campaign's active point and damage class limits.
 
 
Doug
Check out the Breaking Things chapter on p171 of 6e2

Not taking applications.... but I could run this again... let me think about it.

I originally email this response to SinedOL back on Aug 23.  I am reprinting it here for informational sake in case others have similar issues.
 
 

I have a player who premiered his new character: an underwater type, which is an absolute first for any of my groups.  Keeping in mind that we started with 1e, that's a length of time that I feel sufficiently demonstrates our appreciation of the concept. 
 
Breathe under water or in bad atmosphere, density increase, strength, durability, hand-to-hand attacks, and of course, swimming (and lots of it). He's a mutant who can sprout a membrane akin to the fins on a skate (which he  can also use for short-distance gliding) , retractile claws and finger webbing, claws toxic on command. 
 
As we generally don't "respect" the aquaman / namor / prince of Atlantis thing (I mean the group, of course, and not the board at large), he was undergoing some good-natured ribbing from the other characters:
 
So are you from Atlantis? 
Was your mother a mermaid? 
Do you have to stay on the water? 
 
The _player_ was taking it in stride,  but the _character_ was becoming annoyed:
 
"can you talk to fish?" 
"I know a few starfish barks I could share with you...." 
 

Smaller.
 
they get smaller from year to year.  Not just measurably, but _visibly_.  Fortunately for bicyclists, there's a considerable amount of "narrower" involved in that.
 
When I bought the Leviathan, I had been driving a truck that had three full "butt sculpts" in the bench seats.  The Leviathan has two, and a half-one between them.
 
The last time I went truck shopping (I try to replace my truck every twenty years, wether it needs it or not   ), a "full-sized" truck had exactly two butt sculpts and just barely enough room to fold an arm rest between them.
 
Seriously: I don't know if you have the chance regularly, but lay a tape measure across any vehicle that has been in production for years-- they are all much narrower than they were, and getting moreso.  It goes back to the imperative to increase mileage, etc; I get the value of that.  But I don't get the value of a "crew cab" that won't actually fit a crew.  😕
 
Another way to think about it (as far as trucks go):
 
When you were a kid, the wheel wells inside the bad were _massive_.  An adult could sit comfortable on one.  Today, they are barely a flare in the inner wall of the bed.  At once time, you knew you had thirteen inches of "space" in front of and behind that wheel well should you have a stack of plywood or drywall in the bed.  Today you have (depending slightly on brand) about five inches of space there.  You also don't have 52-1/2" between those wheel wells the way you used to.  In the seventies, that dropped to about 50", depending on brand, 49.5.  In the nineties, that dropped to 48.75.  Today, if you have one of those plastic bed liners, you're going to catch grief wedging 48" sheet goods in there.  They'll fit, but you'll work for it.
 
When we bough the wife's car-- last year?  Has it been two years yet?-- I was actually truck shopping.  I was so disgusted by what was passing as a "full sized truck bed" that we just bought her car.   I'm going to have to trade up for a plan we have down the road, but for now, I just can't reconcile the fact that a full sized pick-up truck is slowly (and stupidly) becoming taller than it is wide.  I say "stupidly," because I buy them to work out of.  When you decide the bed needs to go from 16-18 inches deep for 28" deep, it gets harder to reach into them.  Then, for whatever reason, the floor of the bed needs to come up to my hips.....   It makes it extremely difficult to work out of them, and I'm just a smidge over six foot tall!  It's ridiculous.
 
 
Oh-- sorry.   Anyway, cars are getting smaller, and have been since the late seventies.  Compare the "midsized" Ford Granada of old to a freakin' Cadillac today.  It's sad.   It's the whole reason the SUV craze happened:  people come in the same size they used to, and were tired of wedging themselves into increasingly-more-cramped cars to go wherever they needed to go.