I usually use a global variable to scale enemy difficulty, along with a "boss" group (activated when it is time for the boss to appear)
for example I could have a variable called minionhealthscale set to 1.
when creating minions, do this:
loop: 20 times;[/code:2olbnvnu]action[code:2olbnvnu]create: minion at (x,y)[/code:2olbnvnu]action[code:2olbnvnu]set minion.life: =10*minionhealthscale[/code:2olbnvnu] - this makes the minion health correctly when each minion is created
then to activate your boss group:
condition[code:2olbnvnu]minions destroyed: =20[/code:2olbnvnu]action[code:2olbnvnu]set group "boss" enabled[/code:2olbnvnu]
Then your boss group would have these codes in it:
[code:2olbnvnu]various boss creation and attack codes etc[/code:2olbnvnu]
when the boss is defeated:
conditions[code:2olbnvnu]bosshealth < 1;trigger once while true;[/code:2olbnvnu]action[code:2olbnvnu]boss: destroy[/code:2olbnvnu]
action[code:2olbnvnu]set minionhealthscale: =minionhealthscale*10[/code:2olbnvnu]
action[code:2olbnvnu]disable group "boss"[/code:2olbnvnu]
obviously the way you scale minionhealthscale will affect how much more health the minions have each time the boss group activates. Above I have it so that the minion health multiplies by 10 after each boss, so your minions might have 10 health, then 100 health, then 1000 and so on. You could use +10 which would just make it 1 11 21 31 41 etc, or any equation you want to balance your game.
I hope this helped * edit made it clearer and more relevant to your needs