If you are playing a matched play game, you are allowed to have an understrength unit in an Auxiliary Support Detachment. Due to constraints within Battlescribe, we are not able to reflect this in the error checking. To properly calculate your PL and Points, add the unit you want to take as an understrength unit and then open the context menu on each model in the unit you do not want to use via right click or tap and hold. Then delete the model from that context menu. This will permanently display an error in your list, but it will calculate your points correctly.
Instead of moving in their Movement phase, any THOUSAND SONS CHARACTER can, at the end of their Movement phase, attempt to summon a TZEENTCH DAEMON unit with this ability by performing a Daemonic Ritual (the character cannot do so if they arrived as reinforcements this turn). Roll up to 3 dice - this is your summoning roll. You can summon to the battlefield one new TZEENTCH DAEMONS unit that has the Daemonic Ritual ability and a Power Rating equal to or less than the total result. This unit is treated as reinforcements for your army and can be placed anywhere on the battlefield that is wholly within 12" of the character and is more than 9" from any enemy model. If the total rolled is insufficient to summon any unit, the ritual fails and no new unit is summoned. If your summoning roll included any doubles, your character suffers a mortal wound. If it contained any triples, it instead suffers D3 mortal wounds.