Okay, an example:
You go to the "Barracks" and recruit one "Master Sargent" that fills a creature slot. He is alone, so has a base strength of N.
You use him in 1 winning fight, and you may then recruit 1 soldier to follow him. The strength of the "unit" is now (square-root of 2) x N. Formula is N x square-root(1+X) where X is the number of active soldiers following the 1 leader. So each new soldier gives a smaller effective addition to the unit strength.
4 wins gets you #2, 9 gets you #3, 16 gets you #4 and so forth, but you have to go back to the Barracks to actually find them to recruit (costs AP & winertia), the cost going up as the square of the number in line. So each added soldier gets exponentially harder.
If you LOSE a fight, you lose one soldier, but you may go back and recruit a replacement.
You wander through the woods and encounter "poison ivy". One soldier goes on sick call, and can't be replaced, but if you find "calming ointment" then they return to active duty.
So: The Master Sargent works just like a normal crit except he has 3 numbers more - max soldiers, current soldiers, and sick soldiers. His attack is calculated based on the formula N x square-root (1+current-sick).
So the unit could be "Boy Scouts" or "Grasan Daycare" or "Archeologist Party" or "Alien Reconnaisance" or whatever, and the only real difference would be the words, the pictures, and maybe you'd adjust the base stats of the leader depending on flavor.
Not really examined yet which stats would go up with number of soldiers. Attack yes, Defense maybe, others haven't thought it out. I originally assumed physical attacks only, but if it's a coven of witches, it might have non-physical attacks and the power would go up with numbers.