[Nightfall]

Assuming your talking about devils...

I've been using them in my first game pretty effectively, bare minimum group to deploy them in for effectiveness is 10 if you deploy them with some magic support, 15 works much better and with 20 you shouldn't take losses.

Summoning them one by one isn't very efficient though, you are better off using soul contracts or Infernal Forces.

They work best with a flying mage commander as a thug group. Due to the huge morale they can be very effective in battles with attack rear script, but be wary of storm.