Master of the Black Arts Warhammer fantasy battle 8th edition Vampire Counts Vampiric Power
Master of the Black Arts
This is a Vampiric Power that has changed dramatically from 7th edition to 8th edition sadly for the worse. Previously in 7th edition this granted the Vampire with the power 2 extra power dice, it was also cheaper points wise. the increased cost means it is only possible for a Vampire Lord of Strigoi Ghoul King to take this Vampiric Power.
Now in 8th edition it allows you to re roll one of the dice for the Winds of Magic when rolling to see how many power dice are available in the magic phase. In most case 2 extra power dice would have been better, re rolling a low dice runs the risk of getting the same or an even lower result. rolling higher also means it increases the number of dispel dice that your opponent has.
The only saving grace it has is that it can save you from numerous dismal magic phases should you roll a 2 or 3 for the Winds of Magic total.
Pros and cons
Sadly given the high points cost of Master of the Black Arts for a now reduced effect in 8th edition it does some mostly con, a Necromancer with the Forbidden Rod costs only slightly more points and would probably benefit you more on the 1 turn you need the Winds of Magic to be high as well as giving a chance to channel an extra power/dispel dice and have another potential casting of Invocation of Nehek.
Mannfred Von Carstein comes with this ability anyway so if you takehim you may as well make use of the ability, it can save your from repeatedly low rolls on the Winds of Magic (though of course you could just get the same) so it may be of use to you if you intend to rely heavily on magic to secure your victory.
Potentially it is of more use in a Storm of Magic game where you are rolling 4 dice for the Winds of Magic as this increases the chance one of your dice will be a low result.