Mistcaller
Creature — Merfolk Wizard
Sacrifice this creature: Until end of turn, if a nontoken creature would enter and it wasn't cast, exile it instead.
Hospitality is of little concern to those who do not wish to be disturbed.
Ryan Yee
Core Set 2019 Promos (PM19)
• #62sRulings
If Mistcaller enters the battlefield at the same time as other creatures, its ability can’t be activated in time to affect those creatures.
(wotc • 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.
(wotc • 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.
(wotc • 2018-07-13)
Rulings
If Mistcaller enters the battlefield at the same time as other creatures, its ability can’t be activated in time to affect those creatures.
(wotc • 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.
(wotc • 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.
(wotc • 2018-07-13)