While treasure tokens were first introduced to Magic: The Gathering way back in 2017s Ixalan block, it was only during the Norse-mythology themed set Kaldheim released earlier this year that their strength started to really catch the eye of deck-builders
It feels not great for several reasons between being way too narrow most of the time, madness being a little tangential - even if it fits the deck's minor blood theme, and the flavor being off when Avacyn is dead
If the spell being copied has an X whose value was determined as it was cast (like Debt to the Deathless has), the copy has the same value of X
Anecdotally, every blue player I know loathes red
More goodies came with Modern Horizons , where Snow was a major theme of the Blue/Green color combo (Abominable Treefolk), but stretched into other colors, too (On Thin Ice, Dead of Winter)