They trigger prowess, usually cost only 1-2 mana, and also empower your attacking creatures
As a Saga enters, its controller puts a lore counter on it
For example, Complains Clerk has "Whenever you roll a 1, create a 1/1 white Clown Robot artifact creature token." If you choose that ability, you ignore everything up to the first comma, ending up with "Create a 1/1 white Clown Robot artifact creature token." Some triggered abilities have an "intervening if" clausethat is, they are written in the form of "When/Whenever/At [trigger event], if [condition], [effect]." If you choose such an ability with Trigger Happy, you ignore the trigger event, and the ability will go on the stack even if the intervening if condition is not fulfilled, but the ability will still check the intervening if condition as the ability tries to resolve
You won't look at more than one card from your library at once
This makes it easier to get 1 hit knockouts against these Pokmon