Slivdrazi Monstrosity

• WWizards of the Coast2019-11-12
  Official Ruling
  Devoid means “This object is colorless.”
• WWizards of the Coast2019-11-12
  Official Ruling
  If a creature is attacking a planeswalker, the planeswalker’s controller is the defending player.
• WWizards of the Coast2019-11-12
  Official Ruling
  If a creature attacks a planeswalker and that planeswalker leaves the battlefield, the creature continues to attack. If it’s blocked, it’ll deal combat damage as normal, but if it’s unblocked, it won’t deal any combat damage.
• WWizards of the Coast2019-11-12
  Official Ruling
  Annihilator 1 means “Whenever this creature attacks, defending player sacrifices a permanent.”
• WWizards of the Coast2019-11-12
  Official Ruling
  Due to the carefully calibrated system of layers that Magic uses to determine the interaction of continuous effects, gaining an ability that changes the color of an object has no effect on the color of that object. Despite this, Slivdrazi Monstrosity causes Slivers to become colorless as they gain devoid. Rather than try to figure out how this could work, this card should just be played as though it read “Slivers you control have devoid and annihilator 1 and are colorless.”
• WWizards of the Coast2019-11-12
  Official Ruling
  Slivdrazi Monstrosity’s ability affects itself, causing it to become colorless and gain devoid and annihilator 1 while it’s on the battlefield. While not on the battlefield, it’s all colors.
• WWizards of the Coast2019-11-12
  Official Ruling
  can be paid only with one colorless mana.

Rulings via Scryfall