Summon Creature of the Night Warhammer fantasy battle 8th edition Vampire Counts Vampiric Power overview
Summon Creatures of the Night
A Vampire or Vampire Lord with this Vampiric Power enhances his use of the Invocation of Nehek spell. This cheap power allows the Vampire to increase the following units beyond their starting size
The special character Count Mannfred Von Carstein (the lord version of this special character) comes equipped with this Vampiric Power which also synergises well with his Dark Acolyte Vampiric Power.
Pros and cons
Pros are this Vampiric Power is cheap to buy and available to any and all Vampires, Vampire Lords and Strigoi Ghoul Kings in your army. It can also be quite a boost if you are using units of Dire Wolves to protect your more expensive units such as Black Knights or Blood Knights effectively keeping their "shield" intact for longer.
Cons are it is only effective if you have these units in your army, the range of Invocation of Nehek is short without powering it up considerably, this is also compound by the fact that they are amongst the fastest moving units available to Vampire Counts meaning they are more likely to have moved out of range.
A Vampire is also a more expensive choice over a Necromancer whom you might have chosen if you did not want or need this ability.