Ah okay. My bad. I'm still playing through the first cycle so didn't know of any rules about only using 2 heroes. How does that work? And from what expansion did we get that option?
You have that option from the Core Set rules. You are limited to a maximum of 3 heroes, but not to a minimum. Some cards appeared in Dwarrodelf cycle that cost less resources if player has a Threat Level less than 20. These cards have the Secrecy keyword printed.