The skills activate when their activation condition is met. That could be when a hero's health is under 30% (injured), when another hero's health drops under 30% (aid), when the hero kills an enemy (kill), and others!
the thing I dont like is that upgrades are useless. Gold is better spent leveling up armies and getting to the next bonus, and the diamonds are better off in the bank collecting interest and boosting income.
Suggestion: hovering mouse over haste should highlight the item that will be sped up. This would be useful if we want haste to effect daggers, scythes or swords to take the most benefit from using sale.
 "Idle Sword 2"){kind=icon}
 "Insanity Clicker"){kind=icon}
 "Questmore"){kind=icon}
 "Scream Collector"){kind=icon}
 "Idle Wizard"){kind=icon}
 "ARMY MASTERY CLICKER"){kind=icon}
 "Island Defense"){kind=icon}
 "Clicker Troops"){kind=icon}
 "Smith & Smith"){kind=icon}
 "Infinite Hero"){kind=icon}
The skills activate when their activation condition is met. That could be when a hero's health is under 30% (injured), when another hero's health drops under 30% (aid), when the hero kills an enemy (kill), and others!