2018-07-13
If Mistcaller enters the battlefield at the same time as other creatures, its ability can't be activated in time to affect those creatures.
2018-07-13
Mistcaller's ability doesn't stop creature tokens from entering the battlefield. It also doesn't affect creatures that are already on the battlefield.
2018-07-13
Mistcaller's ability won't affect any nontoken creatures that were cast, including ones cast from unusual zones such as your graveyard.