Mirran Safehouse does not have summoning sickness.
({1} magic symbol) available.
Steps
Activate Mirran Safehouse using Mutavault's second ability by paying ({1} magic symbol) , causing Mirran Safehouse to become a 2/2 creature with all creature types until end of turn.
Activate Mirran Safehouse using Griffin Canyon's second ability by tapping it, untapping Mirran Safehouse and giving it +1/+1 until end of turn.
Repeat step 2.
Results
Infinitely large Mirran Safehouse until end of turn.