Mishra's Factory (Preston Poulter) [Pro Tour Collector Set] Centaur Spirit Creatures can't attack you unless

Creatures can't attack you unless their controller pays {2} for each creature they control that's attacking you

Unfortunately

Set: Scourge Type: Enchantment Rarity: Rare Cost: {2}{U} Whenever a creature dies

Set: Zendikar Type: Creature — Merfolk Wizard Ally Rare Cost: {4}{U} {T}: Draw a card for each Ally you control

Mishra's Factory (Preston Poulter) [Pro Tour Collector Set] Centaur Spirit Creatures can't attack you unlessSet: Pro Tour Collector Set Type: Land Rarity: Uncommon {T}: Add {C}. {1}: Mishra's Factory becomes a 2 2 Assembly Worker artifact creature until end of turn. It's still a land. {T}: Target Assembly Worker creature gets +1 +1 until end of turn.