Cactuars 7 mana cost does keep it respectful, but in these days of fast mana and cheating creatures out, its not a stretch to imagine this card being a winning move out of nowhere
Since stores tend to open boxes to sell singles or players open them for packs, it's natural that fans find them easily on the market
Functionally, Yuna's Whistle is a pseudo-cantrip that always replaces itself with a creature, and finding the creature gives you some +1/+1 counters too, so there's combat trick potential as well
Commune with Beavers Yoni Skolnik, the Principal Game Designer who led design vision for this set, pitched this card early on and both Gavin Verhey and I loved it
For each character a player has at The Queens Castle, they can draw a card at the start of their turn