Boon of Boseiju

Instant

Target creature gets +X/+X until end of turn, where X is the greatest mana value among permanents you control. Untap it.

She closed her eyes and remembered the smell of the leaves of Jukai Forest. When she opened them, the buildings of Towashi had grown small.

2022-02-18 If a permanent on the battlefield has {X} in its mana cost, X is 0 when determining that permanent's mana value.
2022-02-18 The greatest mana value among permanents you control is determined as Boon of Boseiju resolves.
2022-02-18 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.

mtg.wtf