Silvanus's Invoker and Serra's Sanctum on the battlefield.
You control at least nine enchantments.
Steps
Activate Serra's Sanctum by tapping it, adding at least nine ({W} magic symbol) .
Activate Silvanus's Invoker by paying ({8} magic symbol) , causing Serra's Sanctum to become a 8/8 Elemental with haste, and untapping Serra's Sanctum.