Thanks for the quick response. I do a couple of types of tests. Overall the most reliable one would indeed be the first stage, and using the cheat which activates all powers.
My other type of tests makes use of an old savegame in Attilan where my characters had reached level 35. This savegame somehow (luckily) always loads after making herostat changes and most of the characters seem to be fully playable, with only a couple of exceptions in that a few characters can't fly. Playing the Paibok mission in the simulator usually gives me a good impression of mod & tinkering playability (- obviously always double-checking with a new game as well).
I just checked it again and I realize that I was partly mistaken as far as the Shield of Night's blocking ability goes - sorry about that. The damage IS reflected as stated, but the attack doesn't seem to be blocked. Black Knight gets 3 damage from an Ultron Warrior whether I use the power or not, if I use the power, the Ultron Warrior receives about 12-17 damage. (Or wasn't a full block intended?)
I haven't seen the Death Threat fail it's instant kill yet... against a normal enemy. I just tested some more up until fighting Scorpion and I did not get an instant kill against him. Now, it may seem obvious that the power's minimum damage suffices for the Ultron Warriors but I don't think it should. It should deal 33-35 damage at minimum level, if I use normal attacks I can see that they can take a bit more than that.
(I am currently using the Realism mod, which means that Scorpion doesn't have his boss_resistance values, so it can't be that.)