The Giovanni and Necromancers have great Master cards and a few other assets. Here are they all detailed for you... Comments and ratings by Arpèges and Orpheus.

Master Card Text
Acquired Ventrue Assets
Put an amount of blood counters (from the blood bank) on this card equal to the number of Giovanni you control. During your master phase, you may move 1 blood from this card to any Giovanni you control. Burn this card if there is no blood on it. This card may be burned by any minion who is not Ventrue as a (D) action..
Very very very useful ! This card is like an investment card, except it DOESN'T count as a master phase to gain blood. Unfortunately it can, and often will, be burned. Play, of course, with blood dolls.
Coroner's Contact
Go through your crypt to find a Samedi vampire. Show it to all players and place it in your uncontrolled region. Move one blood from the blood bank to that uncontrolled Samedi.
A Recruitement for no blood, and a gain of 1 Transfer. Very useful in any deck including a Lone Samedi, or needing the Baron quickly ; correct in any Samedi deck.
Dirty Contract
Master: contract. Put this card on a minion and choose a Samedi in play. The chosen Samedi can enter combat with the minion with this card as a +1 stealth (D) action unless they are controlled by the same Methuselah. This card cannot be played on a Nosferatu or Giovanni. Burn option.
Despite a big flaw (the target restriction), it gives the Samedi the equivalent of the Assamite card. Assassins are cool.

Dis Pater

Unique master. Put this card in play. Once each action, when a Giovanni you control successfully bleeds your prey, you may remove seven cards in your ash heap from the game to give that action +1 bleed.

NICE !! A new vision of the Ash Heap game begins with this card: now we can burn our own ash heap for benefit. Make careful use of it if you need to fetch back some cards, but this can give you the bonus bleed you need to finish your prey in desperate time ! Also note that it is on a succesful bleed, and makes it a good anti-deflection bonus card. Be careful not to become the Table Target when you put it in play...

Glass Walker Pact

Unique master. Put this card in play. During your untap phase, you may burn the top card of your library to move a blood from any ready tapped vampire to a ready Giovanni. If the card you burned is a master card, burn this card as well. Burn this card if another Methuselah controls a werewolf.

This could have been a good card. The thematics are nice, the werewolf condition isn't that bad... But the Master handicap is Huge ! You pay 2 pool and if your first card is a Master, you did it for just a blood ! A Giovanni deck needs its (often great) masters, so the only way to actually play this card is to be able to know which card is on top. Not likely in this clan.

Lazarene Inquisitor
Harbingers of Skulls
Unique Master. Put this card on a ready Harbinger of Skulls you control. The Harbinger of Skulls with this card can burn up to 2 blood from a ready vampire as a +1 stealth (D) action. Any Sabbat vampire can burn this card as a (D) action. Burn option.
Nice card, very combo with baleful dolls, society of leopold, milicent smith (if the target has to hunt…). Steal two blood and Freak Drive is still a gain of one for you, a loss of two for your enemy, and you can act agin. The (D) burn clause orients it towards a Wall deck. The Harbingers now truly take all your ressources, not just your library...
Mausoleum, Venice
Unique location. Tap to gain 2 votes during a political action; if Ventrue Headquarters is in play, you gain only 1 vote.
Not that bad. It is cheap and may help you to balance the game.
Morgue Hunting Ground
Unique location. During your untap phase, a ready vampire you control gains 1 blood from the blood bank. A vampire can gain only 1 blood from Hunting Ground cards each turn.
What else to say ? Who shouldn't play a HG in a deck relying mainly on a clan ?
Path of Bone, The
Unique Master. Put this card in play. Giovanni burn 1 less blood when playing cards that require Necromancy. Any minion may burn this card as a (D) action; if that minion is a vampire, he or she takes 1 damage (damage not preventable) when this card is burned.
Very useful, as necromancy isn't free. But it won't reduce Call of the Hungry Dead in sup, but will give you Whispers, Gear Up, Spectral... for free.. Include only if you play lots of costly Necro cards (and evidently with Shambling Hordes or Pupeteers).

Proxy Kissed

Master: out-of-turn. Put this card on a Giovanni when you move that Giovanni from your uncontrolled region to your ready region during your influence phase. This Giovanni gains one level of Potence and one level of Fortitude. His or her capacity is increased by 1. Move 1 blood from the blood bank to this Giovanni.
So we didn't get a way to make babies as the other indies ? No matter. We can still make them the old-fashioned way. But ours will be better, stronger, bigger : the best, as always ! This great card is of course combo with the For Gios, or to give it to a vamp the turn it is influenced (good in heavy-fighting environments). It also allows all those great 7-Caps to be untapped by Emergency Preparations or Mylan Horseed (Go Carlotta !!) or to find... Golconda, the inner peace !

Regenerative Blood
Unique Master. Put this card on a Samedi you control. The Samedi with this card can heal 2 damage for each blood counter he or she burns. Burn option.
Useful in a heavy warzone environment. Too bad it is unique…
All / Giovanni
+1 stealth action. Requires a ready vampire. Choose one or more younger vampires in torpor. If there are any Gehenna cards in play, the vampires need not be younger. Steal 1 blood from each chosen vampire. If this acting vampire is Giovanni, you may also move one card from your ash heap to your hand for each blood stolen. Discard down to your hand size afterward. Only one Siphon can be played each turn.
Although this card can be played by any vampire, it is obviously meant for the Giovanni ; it was also our "reward" for winning a Storyline !! Not anywhere on the power curve of Baltimore Purge, though : cornercase at best, Siphon will be used in very few aggressive Giovanni decks. It's not that it's bad : just not good enough, and not in tune with the Family's politics in general...
Slaughterhouse, The
Harbingers of Skulls
Location. Tap to burn up to 2 cards from the top of your prey's library. Burn option.
Blind library burning will make your grand prey win the game. Wise library burning will give you the edge on your prey. May be used as a menace too.

Sudario Refraction

+1 stealth action. Choose three cards in your ash heap and move them to the top of your library. Then, discard three cards at random from your hand (and draw up to your hand size afterward).
Niiiiiiiiice ! Now you don't need to have Nec to do some... Just being a Giovanni gives you some advantages, you see. Of course, you'll have to loose some random cards from your hand, but if you know the three you'll get it may be worth it. And it's free !!!

Tower of London
Unique location. When an action requiring Necromancy is successful, tap this location to gain 1 pool.
Not that good. It is expensive. You need to play Giovanni and to play several Nec action cards to gain pool. You must tap it. YOu will begin gaining from it the third turn after you played it, at best… A great way to gain pool in a Shambling Hordes deck, though.
Venitian Conference
Reaction.+2 intercept, only usable when a Camarilla vampire is taking an action.
Very, very marginally useful before Gehenna, it is now more so than ever : +2 Intercept is very good, but Camarilla is less played now, and other cards can give us Intercept. Still, is can make a difference in the right place, at the right time...