Re: Gargoyles HERO
I considered posting this in the Fantasy HERO forum because I had difficulty envisioning a playable campaign outside the medieval "protection pact with humans" setting.
I don't think this poses as much of a problem as "helpless", though; if all (or even just most) of the PC's are gargoyles, the GM can simply run games that only take place at night. If one (or more) of them was captured/relocated overnight, this will become apparent when they awaken. If one (or more) of them gets smashed, they may never wake up at all
This strikes me as more of a "plot device" than game mechanic; a Secret might cover it, but sometimes friends can learn the Secret without sharing it freely, and even enemies might keep it to themselves for a rainy day.
A modern campaign is feasible if the PC's realize and accept that secrecy is paramount - if they fail to maintain it, they may very well die!
The problem is that there are two secrets. One of them is the nature of the gargoyles (that they turn to stone during the day, and are helpless to defend themselves during that time). Another is the exact location they hide in. The latter can change, especially if they realize that they have become Hunted by their enemies (which may include the general public ).
For the first, a Social Limitation modelled after Secret Identity seems appropriate; there may or may not be an extreme risk of death or injury (that could reflect the number of people who want the gargoyles dead, but also by how easily such death or injury might be inflicted upon the gargoyles, and the latter seems more appropriate for that second aspect, namely location), but if exposed it would, in turn, expose the character to attack. But, as noted in the third paragraph, the Secret can be exposed to one without, necessarily, exposure to all. The description of Secret Identity given in the book offers a Severe version only if the character has a large number of enemies who would wish to kill/maim him; this seems to require that the Secret be compromised for everyone.
The second aspect suffers from similar problems; location can be changed overnight, leaving any previously compromised Secret Locations no longer "revealed", in the sense that the gargoyles' current (for that night, and possibly any future nights as well) location is still unknown to others.
I think the two questions go together: for that size, they would need to have hollow bones and be quite fragile inside to "realistically" fly at all, much less glide, and I still think that's pushing "realism" quite a bit
But they are, obviously, quite durable; and, so, I think it appropriate to refer all questioners to the same SFX that justifies nonhuman creatures who turn to stone during the day and revert each night (usually) - magic
For the PD question, I think that's simply "tough as stone" regular (resistant?) PD (or Armor) with the SFX "attacks that deal no damage, bounce".