In fact, I had forgotten that I touched on Pyramid Tests and Stamina in the original ICONS rules, after Team-Up came out. Here's what I said...
One of the optional rules in ICONS Team-Up is that characters can use success pyramids instead of Stamina. That is, instead of saying that a given character has 15 Stamina, you say that he needs a Massive Success to knock out.
Quick recap of terms: A Massive Success means that you get 5 or more points of Effort (that is, your roll and numbers add up to 5 or more better than the target difficulty, whatever it is: a roll+Ability of -1+8=7 is a Massive Success if the difficulty is 2, but not if the difficulty is 10). The thing that makes this a pyramid is that the successes are cumulative: two moderate successes make a major success, and two major successes make a massive success (which means that four moderate successes total up to a massive success).
In some ways, this is the same as Stamina, except that you're not whittling down Stamina points, you're whittling down even more abstract Success Pyramid points or levels. But that very abstraction opens you up to some different possibilities.
Those successes can be in anything. Suppose your heroes are fighting the evil Regenatron ("The Von Neumann New Man"), with Regeneration 10 and Damage Resistance 8, but only Intellect 3.
Aaaaand the powerhouse character (Strength 10!) player didn't show up the last mnute. What you have instead are Looneytunes the shapeshifter and Bob Howard The Duck, the computer-using occultist who has been cursed into the form of an anthropomorphic metrosexual duck.
With a success pyramid, they could take on Regenatron.
Rather than punching (Looneytunes is Strength 3; Bob Howard The Duck, henceforth BHTD, is Strength 1 because, hey, he's a duck), they confuse him into giving up.
Looneytunes begins by working with BHTD to create a dinner date, and Looneytunes assumes the form of an attractive female rabbit. (Well, it works for Bugs Bunny.) Their first scam is to make it think that he's the odd one for not being an anthropomorphic animal....and they get a major success, because it's not bright. They tell it it's supposed to be a sloth. (The GM adds "Gullible" to his list of challenges for Regenatron, and makes a note that a firmware upgrade will remove that later.)
Then they fake it out by claiming it has to go to the office, which it does, trying very hard to stunt its regeneration into transformation, trying to look like a sloth, and it's moving slowly. It's taken in by the office (moderate success), which is why the explosive in the filing cabinet surprises it. (Looneytunes' cosmic power whipped it up.)
Then Looneytunes comes in as Regenatron's "boss" and begins berating it, but Regenatron figures out who he really is (the poor shapeshifter has a tell), and gets mad (the GM is using the rule where a failure wipes out an equivalent success). Regenatron is angry, so it doesn't see the portable hole that BHTD has conjured up and steps in....and the hole leads to the other hole in the ceiling, so poor Regenatron keeps falling faster and faster, while Looneytunes gives it anvils to hold and gets popcorn while eating, right up until BHTD takes the hole out of the floor...
And so on. It rather reminds me of the Marvel Heroic Roleplaying game in that abstraction (though the idea predates that game).
If you were going to use success pyramids for stamina, I'd consider only using them for villains, or major villains.
Though...in a sense, the minion rule in ICONS is kind of a success anthill: minions are removed from the fight by a single success. You could grade opposition by success pyramids...
|Opposition||To Defeat||Possible Difficulty|
|Minion||A single moderate success||To hit value|
|Henchman||Major success||To hit value|
|Villain||Massive success||5, but depends on hero tactics|
|Megavillain||Massive success||8, but depends on hero tactics|
|Cosmic crossover style villain||Massive success||10, but depends on hero tactics|
What it takes away is any concrete idea of what the heck they're doing, and the level of the power matters less. You have to refigure Regeneration and Energy Drain and Affliction.
What it adds is that villains who would normally be invulnerable are now accessible by all sorts of means.