King Darien XLVIII

Other creatures you control get +1/+1.
{3}{G}{W}: Put a +1/+1 counter on King Darien and create a 1/1 white Soldier creature token.
Sacrifice King Darien: Creature tokens you control gain hexproof and indestructible until end of turn.

Dominaria United

Dominaria United Promos

If King Darien XLVIII leaves the battlefield, other creatures you control immediately lose the +1/+1 bonus. Notably, this means that if you activate its last ability after a creature has already been dealt damage, it might die due to having lethal damage before the ability resolves and gives it indestructible.

In most cases where the value of X isn’t defined in the text of a card, its controller chooses the value of X. However, the X in King Darien’s name is always 10.