Warbreak Trumpeter
Creature — Goblin
Morph 
When this creature is turned face up, create X 1/1 red Goblin creature tokens.
Dany Orizio
Legions (LGN)
• #116Rulings
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)
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)
Rulings
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)
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)