Ideas just keep coming to me.

Summoning Angels

There are no tomes on summoning the messengers, warriors and right hands of the gods. Their feathery wings keep them from having to touch the earth for a reason. They were never meant to be summoned by mortals or Sorcerers of any kind.

However, Demons, through showing how to summon from Hell, have allowed some cunning Sorcerers to work out the arcane geometry and mathematics and poetry that allows mortals to summon Angels. It is difficult and many accomplished Summoners would summon the foulest creature from the pit of nine hells before summoning an angel.

The CTN is doubled from what the numers add up to and the penalty for aging is doubled again if the Sorcerer fails their Aging Roll.

Once an Angel is summoned, the circle to keep them and spells to Banish them should be well in hand. Demons and Devils are always looking for another soul, even at their most angry they see an opportunity. Angels only want to serve their Deity. If they are pulled from their duties they are likely to take a fiery sword to the summoner.

The cause for summoning them had better be noble and without any gain to the caster. Even if banished successfully, an Angel can always petition their diety to go to earth and smite a sinner. Make sure that sinner isn't you.