Hidetsugu Consumes All

A transforming double-faced card enters the battlefield with its front face up by default, unless a spell or ability instructs you to put it onto the battlefield transformed or you cast it transformed, in which case it enters with its back face up.

Each face of a transforming double-faced card has its own set of characteristics: name, types, subtypes, abilities, and so on. While a transforming double-faced permanent is on the battlefield, consider only the characteristics of the face that's currently up. The other set of characteristics is ignored.

Each transforming double-faced card in this set is cast face up. In every zone other than the battlefield, consider only the characteristics of its front face. If it is on the battlefield, consider only the characteristics of the face that's up; the other face's characteristics are ignored.

If Vessel of the All-Consuming is dealt lethal damage at the same time it deals damage, it will be destroyed before the first triggered ability resolves, so the +1/+1 counter won't be put on it in time to potentially save it.

If a permanent on the battlefield has in its mana value, X is 0.

If you are instructed to put a card that isn't a double-faced card onto the battlefield transformed, it will not enter the battlefield at all. In that case, it stays in the zone it was previously in. For example, if a single-faced card is a copy of Azusa's Many Journeys, the chapter III ability will cause it to be exiled and then remain in exile.

The back face of a transforming double-faced card usually has a color indicator that defines its color.

The mana value of a transforming double-faced card is the mana value of its front face, no matter which face is up.

The mana value of a transforming double-faced card with its back face up is the mana value of the front face.

Vessel of the All-Consuming's first triggered ability will trigger whenever it deals any damage, not just combat damage. If it deals damage to multiple players and/or permanents at the same time (perhaps because of trample or because it was blocked by multiple creatures), that ability triggers only once.