This effect is mandatory and can activate during the Damage Step.
This effect does not activate if Reborn Tengu is returned from the field to the Deck.
This effect does not activate if Reborn Tengu is removed from the field while face-down.
source: http://yugioh.wikia.com/wiki/Card_Rulings%3AReborn_Tengu
this part is for the xyz ruling!(location:4th paragraph,half way in)
you have to reconcile all of this with cards like Reborn Tengu that cannot activate their “leaves the field” effect when they are returned from the field to the Deck even though they clearly had to leave to get there. That’s why we included the section on “leaves the field”.
source: http://www.konami.com/yugioh/articles/?p=3195
This effect does not activate if Reborn Tengu is returned from the field to the Deck.
This effect does not activate if Reborn Tengu is removed from the field while face-down.
source: http://yugioh.wikia.com/wiki/Card_Rulings%3AReborn_Tengu
this part is for the xyz ruling!(location:4th paragraph,half way in)
you have to reconcile all of this with cards like Reborn Tengu that cannot activate their “leaves the field” effect when they are returned from the field to the Deck even though they clearly had to leave to get there. That’s why we included the section on “leaves the field”.
source: http://www.konami.com/yugioh/articles/?p=3195