Rakdos Reanimator is a near-mirror in speed — they can win on turn one with Reanimate plus Griselbrand or Atraxa, and they strip your hand with Thoughtseize, Unmask, and Cabal Therapy. Veil of Summer is a reasonable consideration to protect your combo turn against their black disruption, but it requires holding up one mana which can cost you a turn of speed, and Thoughtseize into their hand to strip Shallow Grave or a reanimation piece is more proactive. Hexing Squelcher is too slow for this speed-race matchup. Bringing in the extra Beseech and Echo gives you more combo redundancy after their discard strips pieces. The key is to go off before they assemble a Griselbrand to draw seven and refuel — if they get Griselbrand down, they can easily Cabal Therapy your win conditions out of your hand in response to your combo.