Bane of the Living
Creature — Insect
Morph 
(You may cast this card face down as a 2/2 creature for 
. Turn it face up any time for its morph cost.)
When this creature is turned face up, all creatures get -X/-X until end of turn.
Filip Burburan
Commander 2019 (C19)
• #104Rulings
The X in the ability has the same value as the X paid in the Morph ability. This is pretty easy to derive since there is no other source of X.
(wotc • 2004-10-04)
The trigger occurs when you use the Morph ability to turn the card face up, or when an effect turns it face up. It will not trigger on being revealed or on leaving the battlefield.
(wotc • 2004-10-04)
Rulings
The X in the ability has the same value as the X paid in the Morph ability. This is pretty easy to derive since there is no other source of X.
(wotc • 2004-10-04)
The trigger occurs when you use the Morph ability to turn the card face up, or when an effect turns it face up. It will not trigger on being revealed or on leaving the battlefield.
(wotc • 2004-10-04)