Target creature gets +X/+X until end of turn, where X is the greatest mana value among permanents you control. Untap it.
If a permanent on the battlefield has {X} in its mana cost, X is 0 when determining that permanent's mana value.
The greatest mana value among permanents you control is determined as Boon of Boseiju resolves.
Transforming double-faced permanents, such as those found in this set, have the mana value of their front face at all times, even while back-face-up.